better message when notebook format is not supported

Different messages for bad version and bad JSON.

closes  #1592

IPython/html/services/notebooks/filenbmanager.py

@@ -1,358 +1,359 b''
 """A notebook manager that uses the local file system for storage.
 
 Authors:
 
 * Brian Granger
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import datetime
 import io
 import os
 import glob
 import shutil
 from unicodedata import normalize
 
 from tornado import web
 
 from .nbmanager import NotebookManager
 from IPython.nbformat import current
 from IPython.utils.traitlets import Unicode, Dict, Bool, TraitError
 from IPython.utils import tz
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 
 class FileNotebookManager(NotebookManager):
     
     save_script = Bool(False, config=True,
         help="""Automatically create a Python script when saving the notebook.
         
         For easier use of import, %run and %load across notebooks, a
         <notebook-name>.py script will be created next to any
         <notebook-name>.ipynb on each save.  This can also be set with the
         short `--script` flag.
         """
     )
     
     checkpoint_dir = Unicode(config=True,
         help="""The location in which to keep notebook checkpoints
         
         By default, it is notebook-dir/.ipynb_checkpoints
         """
     )
     def _checkpoint_dir_default(self):
         return os.path.join(self.notebook_dir, '.ipynb_checkpoints')
     
     def _checkpoint_dir_changed(self, name, old, new):
         """do a bit of validation of the checkpoint dir"""
         if not os.path.isabs(new):
             # If we receive a non-absolute path, make it absolute.
             abs_new = os.path.abspath(new)
             self.checkpoint_dir = abs_new
             return
         if os.path.exists(new) and not os.path.isdir(new):
             raise TraitError("checkpoint dir %r is not a directory" % new)
         if not os.path.exists(new):
             self.log.info("Creating checkpoint dir %s", new)
             try:
                 os.mkdir(new)
             except:
                 raise TraitError("Couldn't create checkpoint dir %r" % new)
     
     filename_ext = Unicode(u'.ipynb')
 
     # Map notebook names to notebook_ids
     rev_mapping = Dict()
     
     def get_notebook_names(self):
         """List all notebook names in the notebook dir."""
         names = glob.glob(os.path.join(self.notebook_dir,
                                        '*' + self.filename_ext))
         names = [normalize('NFC', os.path.splitext(os.path.basename(name))[0])
                  for name in names]
         return names
 
     def list_notebooks(self):
         """List all notebooks in the notebook dir."""
         names = self.get_notebook_names()
 
         data = []
         for name in names:
             if name not in self.rev_mapping:
                 notebook_id = self.new_notebook_id(name)
             else:
                 notebook_id = self.rev_mapping[name]
             data.append(dict(notebook_id=notebook_id,name=name))
         data = sorted(data, key=lambda item: item['name'])
         return data
 
     def new_notebook_id(self, name):
         """Generate a new notebook_id for a name and store its mappings."""
         notebook_id = super(FileNotebookManager, self).new_notebook_id(name)
         self.rev_mapping[name] = notebook_id
         return notebook_id
 
     def delete_notebook_id(self, notebook_id):
         """Delete a notebook's id in the mapping."""
         name = self.mapping[notebook_id]
         super(FileNotebookManager, self).delete_notebook_id(notebook_id)
         del self.rev_mapping[name]
 
     def notebook_exists(self, notebook_id):
         """Does a notebook exist?"""
         exists = super(FileNotebookManager, self).notebook_exists(notebook_id)
         if not exists:
             return False
         path = self.get_path_by_name(self.mapping[notebook_id])
         return os.path.isfile(path)
     
     def get_name(self, notebook_id):
         """get a notebook name, raising 404 if not found"""
         try:
             name = self.mapping[notebook_id]
         except KeyError:
             raise web.HTTPError(404, u'Notebook does not exist: %s' % notebook_id)
         return name
 
     def get_path(self, notebook_id):
         """Return a full path to a notebook given its notebook_id."""
         name = self.get_name(notebook_id)
         return self.get_path_by_name(name)
 
     def get_path_by_name(self, name):
         """Return a full path to a notebook given its name."""
         filename = name + self.filename_ext
         path = os.path.join(self.notebook_dir, filename)
         return path
 
     def read_notebook_object_from_path(self, path):
         """read a notebook object from a path"""
         info = os.stat(path)
         last_modified = tz.utcfromtimestamp(info.st_mtime)
         with open(path,'r') as f:
             s = f.read()
             try:
                 # v1 and v2 and json in the .ipynb files.
                 nb = current.reads(s, u'json')
-            except Exception as e:
-                raise web.HTTPError(500, u'Unreadable JSON notebook: %s' % e)
+            except ValueError as e:
+                msg = u"Unreadable Notebook: %s" % e
+                raise web.HTTPError(400, msg, reason=msg)
         return last_modified, nb
     
     def read_notebook_object(self, notebook_id):
         """Get the Notebook representation of a notebook by notebook_id."""
         path = self.get_path(notebook_id)
         if not os.path.isfile(path):
             raise web.HTTPError(404, u'Notebook does not exist: %s' % notebook_id)
         last_modified, nb = self.read_notebook_object_from_path(path)
         # Always use the filename as the notebook name.
         # Eventually we will get rid of the notebook name in the metadata
         # but for now, that name is just an empty string. Until the notebooks
         # web service knows about names in URLs we still pass the name
         # back to the web app using the metadata though.
         nb.metadata.name = os.path.splitext(os.path.basename(path))[0]
         return last_modified, nb
     
     def write_notebook_object(self, nb, notebook_id=None):
         """Save an existing notebook object by notebook_id."""
         try:
             new_name = normalize('NFC', nb.metadata.name)
         except AttributeError:
             raise web.HTTPError(400, u'Missing notebook name')
 
         if notebook_id is None:
             notebook_id = self.new_notebook_id(new_name)
 
         if notebook_id not in self.mapping:
             raise web.HTTPError(404, u'Notebook does not exist: %s' % notebook_id)
 
         old_name = self.mapping[notebook_id]
         old_checkpoints = self.list_checkpoints(notebook_id)        
         path = self.get_path_by_name(new_name)
 
         # Right before we save the notebook, we write an empty string as the
         # notebook name in the metadata. This is to prepare for removing
         # this attribute entirely post 1.0. The web app still uses the metadata
         # name for now.
         nb.metadata.name = u''
 
         try:
             self.log.debug("Autosaving notebook %s", path)
             with open(path,'w') as f:
                 current.write(nb, f, u'json')
         except Exception as e:
             raise web.HTTPError(400, u'Unexpected error while autosaving notebook: %s' % e)
 
         # save .py script as well
         if self.save_script:
             pypath = os.path.splitext(path)[0] + '.py'
             self.log.debug("Writing script %s", pypath)
             try:
                 with io.open(pypath,'w', encoding='utf-8') as f:
                     current.write(nb, f, u'py')
             except Exception as e:
                 raise web.HTTPError(400, u'Unexpected error while saving notebook as script: %s' % e)
         
         # remove old files if the name changed
         if old_name != new_name:
             # update mapping
             self.mapping[notebook_id] = new_name
             self.rev_mapping[new_name] = notebook_id
             del self.rev_mapping[old_name]
             
             # remove renamed original, if it exists
             old_path = self.get_path_by_name(old_name)
             if os.path.isfile(old_path):
                 self.log.debug("unlinking notebook %s", old_path)
                 os.unlink(old_path)
             
             # cleanup old script, if it exists
             if self.save_script:
                 old_pypath = os.path.splitext(old_path)[0] + '.py'
                 if os.path.isfile(old_pypath):
                     self.log.debug("unlinking script %s", old_pypath)
                     os.unlink(old_pypath)
             
             # rename checkpoints to follow file
             for cp in old_checkpoints:
                 checkpoint_id = cp['checkpoint_id']
                 old_cp_path = self.get_checkpoint_path_by_name(old_name, checkpoint_id)
                 new_cp_path = self.get_checkpoint_path_by_name(new_name, checkpoint_id)
                 if os.path.isfile(old_cp_path):
                     self.log.debug("renaming checkpoint %s -> %s", old_cp_path, new_cp_path)
                     os.rename(old_cp_path, new_cp_path)
             
         return notebook_id
 
     def delete_notebook(self, notebook_id):
         """Delete notebook by notebook_id."""
         nb_path = self.get_path(notebook_id)
         if not os.path.isfile(nb_path):
             raise web.HTTPError(404, u'Notebook does not exist: %s' % notebook_id)
         
         # clear checkpoints
         for checkpoint in self.list_checkpoints(notebook_id):
             checkpoint_id = checkpoint['checkpoint_id']
             path = self.get_checkpoint_path(notebook_id, checkpoint_id)
             self.log.debug(path)
             if os.path.isfile(path):
                 self.log.debug("unlinking checkpoint %s", path)
                 os.unlink(path)
         
         self.log.debug("unlinking notebook %s", nb_path)
         os.unlink(nb_path)
         self.delete_notebook_id(notebook_id)
 
     def increment_filename(self, basename):
         """Return a non-used filename of the form basename<int>.
         
         This searches through the filenames (basename0, basename1, ...)
         until is find one that is not already being used. It is used to
         create Untitled and Copy names that are unique.
         """
         i = 0
         while True:
             name = u'%s%i' % (basename,i)
             path = self.get_path_by_name(name)
             if not os.path.isfile(path):
                 break
             else:
                 i = i+1
         return name
     
     # Checkpoint-related utilities
     
     def get_checkpoint_path_by_name(self, name, checkpoint_id):
         """Return a full path to a notebook checkpoint, given its name and checkpoint id."""
         filename = u"{name}-{checkpoint_id}{ext}".format(
             name=name,
             checkpoint_id=checkpoint_id,
             ext=self.filename_ext,
         )
         path = os.path.join(self.checkpoint_dir, filename)
         return path
     
     def get_checkpoint_path(self, notebook_id, checkpoint_id):
         """find the path to a checkpoint"""
         name = self.get_name(notebook_id)
         return self.get_checkpoint_path_by_name(name, checkpoint_id)
     
     def get_checkpoint_info(self, notebook_id, checkpoint_id):
         """construct the info dict for a given checkpoint"""
         path = self.get_checkpoint_path(notebook_id, checkpoint_id)
         stats = os.stat(path)
         last_modified = tz.utcfromtimestamp(stats.st_mtime)
         info = dict(
             checkpoint_id = checkpoint_id,
             last_modified = last_modified,
         )
         
         return info
         
     # public checkpoint API
     
     def create_checkpoint(self, notebook_id):
         """Create a checkpoint from the current state of a notebook"""
         nb_path = self.get_path(notebook_id)
         # only the one checkpoint ID:
         checkpoint_id = u"checkpoint"
         cp_path = self.get_checkpoint_path(notebook_id, checkpoint_id)
         self.log.debug("creating checkpoint for notebook %s", notebook_id)
         if not os.path.exists(self.checkpoint_dir):
             os.mkdir(self.checkpoint_dir)
         shutil.copy2(nb_path, cp_path)
         
         # return the checkpoint info
         return self.get_checkpoint_info(notebook_id, checkpoint_id)
     
     def list_checkpoints(self, notebook_id):
         """list the checkpoints for a given notebook
         
         This notebook manager currently only supports one checkpoint per notebook.
         """
         checkpoint_id = u"checkpoint"
         path = self.get_checkpoint_path(notebook_id, checkpoint_id)
         if not os.path.exists(path):
             return []
         else:
             return [self.get_checkpoint_info(notebook_id, checkpoint_id)]
         
     
     def restore_checkpoint(self, notebook_id, checkpoint_id):
         """restore a notebook to a checkpointed state"""
         self.log.info("restoring Notebook %s from checkpoint %s", notebook_id, checkpoint_id)
         nb_path = self.get_path(notebook_id)
         cp_path = self.get_checkpoint_path(notebook_id, checkpoint_id)
         if not os.path.isfile(cp_path):
             self.log.debug("checkpoint file does not exist: %s", cp_path)
             raise web.HTTPError(404,
                 u'Notebook checkpoint does not exist: %s-%s' % (notebook_id, checkpoint_id)
             )
         # ensure notebook is readable (never restore from an unreadable notebook)
         last_modified, nb = self.read_notebook_object_from_path(cp_path)
         shutil.copy2(cp_path, nb_path)
         self.log.debug("copying %s -> %s", cp_path, nb_path)
     
     def delete_checkpoint(self, notebook_id, checkpoint_id):
         """delete a notebook's checkpoint"""
         path = self.get_checkpoint_path(notebook_id, checkpoint_id)
         if not os.path.isfile(path):
             raise web.HTTPError(404,
                 u'Notebook checkpoint does not exist: %s-%s' % (notebook_id, checkpoint_id)
             )
         self.log.debug("unlinking %s", path)
         os.unlink(path)
     
     def info_string(self):
         return "Serving notebooks from local directory: %s" % self.notebook_dir

IPython/html/static/notebook/js/notebook.js

@@ -1,2037 +1,2037 b''
 //----------------------------------------------------------------------------
 //  Copyright (C) 2008-2011  The IPython Development Team
 //
 //  Distributed under the terms of the BSD License.  The full license is in
 //  the file COPYING, distributed as part of this software.
 //----------------------------------------------------------------------------
 
 //============================================================================
 // Notebook
 //============================================================================
 
 var IPython = (function (IPython) {
 
     var utils = IPython.utils;
     var key   = IPython.utils.keycodes;
 
     /**
      * A notebook contains and manages cells.
      * 
      * @class Notebook
      * @constructor
      * @param {String} selector A jQuery selector for the notebook's DOM element
      * @param {Object} [options] A config object
      */
     var Notebook = function (selector, options) {
         var options = options || {};
         this._baseProjectUrl = options.baseProjectUrl;
         this.read_only = options.read_only || IPython.read_only;
 
         this.element = $(selector);
         this.element.scroll();
         this.element.data("notebook", this);
         this.next_prompt_number = 1;
         this.kernel = null;
         this.clipboard = null;
         this.undelete_backup = null;
         this.undelete_index = null;
         this.undelete_below = false;
         this.paste_enabled = false;
         this.set_dirty(false);
         this.metadata = {};
         this._checkpoint_after_save = false;
         this.last_checkpoint = null;
         this.autosave_interval = 0;
         this.autosave_timer = null;
         // autosave *at most* every two minutes
         this.minimum_autosave_interval = 120000;
         // single worksheet for now
         this.worksheet_metadata = {};
         this.control_key_active = false;
         this.notebook_id = null;
         this.notebook_name = null;
         this.notebook_name_blacklist_re = /[\/\\:]/;
         this.nbformat = 3 // Increment this when changing the nbformat
         this.nbformat_minor = 0 // Increment this when changing the nbformat
         this.style();
         this.create_elements();
         this.bind_events();
     };
 
     /**
      * Tweak the notebook's CSS style.
      * 
      * @method style
      */
     Notebook.prototype.style = function () {
         $('div#notebook').addClass('border-box-sizing');
     };
 
     /**
      * Get the root URL of the notebook server.
      * 
      * @method baseProjectUrl
      * @return {String} The base project URL
      */
     Notebook.prototype.baseProjectUrl = function(){
         return this._baseProjectUrl || $('body').data('baseProjectUrl');
     };
 
     /**
      * Create an HTML and CSS representation of the notebook.
      * 
      * @method create_elements
      */
     Notebook.prototype.create_elements = function () {
         // We add this end_space div to the end of the notebook div to:
         // i) provide a margin between the last cell and the end of the notebook
         // ii) to prevent the div from scrolling up when the last cell is being
         // edited, but is too low on the page, which browsers will do automatically.
         var that = this;
         this.container = $("<div/>").addClass("container").attr("id", "notebook-container");
         var end_space = $('<div/>').addClass('end_space');
         end_space.dblclick(function (e) {
             if (that.read_only) return;
             var ncells = that.ncells();
             that.insert_cell_below('code',ncells-1);
         });
         this.element.append(this.container);
         this.container.append(end_space);
         $('div#notebook').addClass('border-box-sizing');
     };
 
     /**
      * Bind JavaScript events: key presses and custom IPython events.
      * 
      * @method bind_events
      */
     Notebook.prototype.bind_events = function () {
         var that = this;
 
         $([IPython.events]).on('set_next_input.Notebook', function (event, data) {
             var index = that.find_cell_index(data.cell);
             var new_cell = that.insert_cell_below('code',index);
             new_cell.set_text(data.text);
             that.dirty = true;
         });
 
         $([IPython.events]).on('set_dirty.Notebook', function (event, data) {
             that.dirty = data.value;
         });
 
         $([IPython.events]).on('select.Cell', function (event, data) {
             var index = that.find_cell_index(data.cell);
             that.select(index);
         });
         
         $([IPython.events]).on('status_autorestarting.Kernel', function () {
             IPython.dialog.modal({
                 title: "Kernel Restarting",
                 body: "The kernel appears to have died. It will restart automatically.",
                 buttons: {
                     OK : {
                         class : "btn-primary"
                     }
                 }
             });
         });
 
 
         $(document).keydown(function (event) {
             // console.log(event);
             if (that.read_only) return true;
 
             // Save (CTRL+S) or (AppleKey+S)
             //metaKey = applekey on mac
             if ((event.ctrlKey || event.metaKey) && event.keyCode==83) {
                 that.save_checkpoint();
                 event.preventDefault();
                 return false;
             } else if (event.which === key.ESC) {
                 // Intercept escape at highest level to avoid closing
                 // websocket connection with firefox
                 IPython.pager.collapse();
                 event.preventDefault();
             } else if (event.which === key.SHIFT) {
                 // ignore shift keydown
                 return true;
             }
             if (event.which === key.UPARROW && !event.shiftKey) {
                 var cell = that.get_selected_cell();
                 if (cell && cell.at_top()) {
                     event.preventDefault();
                     that.select_prev();
                 };
             } else if (event.which === key.DOWNARROW && !event.shiftKey) {
                 var cell = that.get_selected_cell();
                 if (cell && cell.at_bottom()) {
                     event.preventDefault();
                     that.select_next();
                 };
             } else if (event.which === key.ENTER && event.shiftKey) {
                 that.execute_selected_cell();
                 return false;
             } else if (event.which === key.ENTER && event.altKey) {
                 // Execute code cell, and insert new in place
                 that.execute_selected_cell();
                  // Only insert a new cell, if we ended up in an already populated cell
                 if (/\S/.test(that.get_selected_cell().get_text()) == true) {
                     that.insert_cell_above('code');
                 }
                 return false;
             } else if (event.which === key.ENTER && event.ctrlKey) {
                 that.execute_selected_cell({terminal:true});
                 return false;
             } else if (event.which === 77 && event.ctrlKey && that.control_key_active == false) {
                 that.control_key_active = true;
                 return false;
             } else if (event.which === 88 && that.control_key_active) {
                 // Cut selected cell = x
                 that.cut_cell();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 67 && that.control_key_active) {
                 // Copy selected cell = c
                 that.copy_cell();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 86 && that.control_key_active) {
                 // Paste below selected cell = v
                 that.paste_cell_below();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 68 && that.control_key_active) {
                 // Delete selected cell = d
                 that.delete_cell();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 65 && that.control_key_active) {
                 // Insert code cell above selected = a
                 that.insert_cell_above('code');
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 66 && that.control_key_active) {
                 // Insert code cell below selected = b
                 that.insert_cell_below('code');
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 89 && that.control_key_active) {
                 // To code = y
                 that.to_code();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 77 && that.control_key_active) {
                 // To markdown = m
                 that.to_markdown();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 84 && that.control_key_active) {
                 // To Raw = t
                 that.to_raw();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 49 && that.control_key_active) {
                 // To Heading 1 = 1
                 that.to_heading(undefined, 1);
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 50 && that.control_key_active) {
                 // To Heading 2 = 2
                 that.to_heading(undefined, 2);
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 51 && that.control_key_active) {
                 // To Heading 3 = 3
                 that.to_heading(undefined, 3);
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 52 && that.control_key_active) {
                 // To Heading 4 = 4
                 that.to_heading(undefined, 4);
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 53 && that.control_key_active) {
                 // To Heading 5 = 5
                 that.to_heading(undefined, 5);
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 54 && that.control_key_active) {
                 // To Heading 6 = 6
                 that.to_heading(undefined, 6);
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 79 && that.control_key_active) {
                 // Toggle output = o
                 if (event.shiftKey){
                     that.toggle_output_scroll();
                 } else {
                     that.toggle_output();
                 }
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 83 && that.control_key_active) {
                 // Save notebook = s
                 that.save_checkpoint();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 74 && that.control_key_active) {
                 // Move cell down = j
                 that.move_cell_down();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 75 && that.control_key_active) {
                 // Move cell up = k
                 that.move_cell_up();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 80 && that.control_key_active) {
                 // Select previous = p
                 that.select_prev();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 78 && that.control_key_active) {
                 // Select next = n
                 that.select_next();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 76 && that.control_key_active) {
                 // Toggle line numbers = l
                 that.cell_toggle_line_numbers();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 73 && that.control_key_active) {
                 // Interrupt kernel = i
                 that.kernel.interrupt();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 190 && that.control_key_active) {
                 // Restart kernel = .  # matches qt console
                 that.restart_kernel();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 72 && that.control_key_active) {
                 // Show keyboard shortcuts = h
                 IPython.quick_help.show_keyboard_shortcuts();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 90 && that.control_key_active) {
                 // Undo last cell delete = z
                 that.undelete();
                 that.control_key_active = false;
                 return false;
             } else if (event.which === 189 && that.control_key_active) {
                 // Split cell = -
                 that.split_cell();
                 that.control_key_active = false;
                 return false;                                               
             } else if (that.control_key_active) {
                 that.control_key_active = false;
                 return true;
             }
             return true;
         });
         
         var collapse_time = function(time){
             var app_height = $('#ipython-main-app').height(); // content height
             var splitter_height = $('div#pager_splitter').outerHeight(true);
             var new_height = app_height - splitter_height;
             that.element.animate({height : new_height + 'px'}, time);
         }
 
         this.element.bind('collapse_pager', function (event,extrap) {
             var time = (extrap != undefined) ? ((extrap.duration != undefined ) ? extrap.duration : 'fast') : 'fast';
             collapse_time(time);
         });
 
         var expand_time = function(time) {
             var app_height = $('#ipython-main-app').height(); // content height
             var splitter_height = $('div#pager_splitter').outerHeight(true);
             var pager_height = $('div#pager').outerHeight(true);
             var new_height = app_height - pager_height - splitter_height;
             that.element.animate({height : new_height + 'px'}, time);
         }
 
         this.element.bind('expand_pager', function (event, extrap) {
             var time = (extrap != undefined) ? ((extrap.duration != undefined ) ? extrap.duration : 'fast') : 'fast';
             expand_time(time);
         });
         
         // Firefox 22 broke $(window).on("beforeunload")
         // I'm not sure why or how.
         window.onbeforeunload = function (e) {
             // TODO: Make killing the kernel configurable.
             var kill_kernel = false;
             if (kill_kernel) {
                 that.kernel.kill();
             }
             // if we are autosaving, trigger an autosave on nav-away.
             // still warn, because if we don't the autosave may fail.
             if (that.dirty && ! that.read_only) {
                 if ( that.autosave_interval ) {
                     that.save_notebook();
                     return "Autosave in progress, latest changes may be lost.";
                 } else {
                     return "Unsaved changes will be lost.";
                 }
             };
             // Null is the *only* return value that will make the browser not
             // pop up the "don't leave" dialog.
             return null;
         };
     };
 
     /**
      * Set the dirty flag, and trigger the set_dirty.Notebook event
      * 
      * @method set_dirty
      */
     Notebook.prototype.set_dirty = function (value) {
         if (value === undefined) {
             value = true;
         }
         if (this.dirty == value) {
             return;
         }
         $([IPython.events]).trigger('set_dirty.Notebook', {value: value});
     };
 
     /**
      * Scroll the top of the page to a given cell.
      * 
      * @method scroll_to_cell
      * @param {Number} cell_number An index of the cell to view
      * @param {Number} time Animation time in milliseconds
      * @return {Number} Pixel offset from the top of the container
      */
     Notebook.prototype.scroll_to_cell = function (cell_number, time) {
         var cells = this.get_cells();
         var time = time || 0;
         cell_number = Math.min(cells.length-1,cell_number);
         cell_number = Math.max(0             ,cell_number);
         var scroll_value = cells[cell_number].element.position().top-cells[0].element.position().top ;
         this.element.animate({scrollTop:scroll_value}, time);
         return scroll_value;
     };
 
     /**
      * Scroll to the bottom of the page.
      * 
      * @method scroll_to_bottom
      */
     Notebook.prototype.scroll_to_bottom = function () {
         this.element.animate({scrollTop:this.element.get(0).scrollHeight}, 0);
     };
 
     /**
      * Scroll to the top of the page.
      * 
      * @method scroll_to_top
      */
     Notebook.prototype.scroll_to_top = function () {
         this.element.animate({scrollTop:0}, 0);
     };
 
 
     // Cell indexing, retrieval, etc.
 
     /**
      * Get all cell elements in the notebook.
      * 
      * @method get_cell_elements
      * @return {jQuery} A selector of all cell elements
      */
     Notebook.prototype.get_cell_elements = function () {
         return this.container.children("div.cell");
     };
 
     /**
      * Get a particular cell element.
      * 
      * @method get_cell_element
      * @param {Number} index An index of a cell to select
      * @return {jQuery} A selector of the given cell.
      */
     Notebook.prototype.get_cell_element = function (index) {
         var result = null;
         var e = this.get_cell_elements().eq(index);
         if (e.length !== 0) {
             result = e;
         }
         return result;
     };
 
     /**
      * Count the cells in this notebook.
      * 
      * @method ncells
      * @return {Number} The number of cells in this notebook
      */
     Notebook.prototype.ncells = function () {
         return this.get_cell_elements().length;
     };
 
     /**
      * Get all Cell objects in this notebook.
      * 
      * @method get_cells
      * @return {Array} This notebook's Cell objects
      */
     // TODO: we are often calling cells as cells()[i], which we should optimize
     // to cells(i) or a new method.
     Notebook.prototype.get_cells = function () {
         return this.get_cell_elements().toArray().map(function (e) {
             return $(e).data("cell");
         });
     };
 
     /**
      * Get a Cell object from this notebook.
      * 
      * @method get_cell
      * @param {Number} index An index of a cell to retrieve
      * @return {Cell} A particular cell
      */
     Notebook.prototype.get_cell = function (index) {
         var result = null;
         var ce = this.get_cell_element(index);
         if (ce !== null) {
             result = ce.data('cell');
         }
         return result;
     }
 
     /**
      * Get the cell below a given cell.
      * 
      * @method get_next_cell
      * @param {Cell} cell The provided cell
      * @return {Cell} The next cell
      */
     Notebook.prototype.get_next_cell = function (cell) {
         var result = null;
         var index = this.find_cell_index(cell);
         if (this.is_valid_cell_index(index+1)) {
             result = this.get_cell(index+1);
         }
         return result;
     }
 
     /**
      * Get the cell above a given cell.
      * 
      * @method get_prev_cell
      * @param {Cell} cell The provided cell
      * @return {Cell} The previous cell
      */
     Notebook.prototype.get_prev_cell = function (cell) {
         // TODO: off-by-one
         // nb.get_prev_cell(nb.get_cell(1)) is null
         var result = null;
         var index = this.find_cell_index(cell);
         if (index !== null && index > 1) {
             result = this.get_cell(index-1);
         }
         return result;
     }
     
     /**
      * Get the numeric index of a given cell.
      * 
      * @method find_cell_index
      * @param {Cell} cell The provided cell
      * @return {Number} The cell's numeric index
      */
     Notebook.prototype.find_cell_index = function (cell) {
         var result = null;
         this.get_cell_elements().filter(function (index) {
             if ($(this).data("cell") === cell) {
                 result = index;
             };
         });
         return result;
     };
 
     /**
      * Get a given index , or the selected index if none is provided.
      * 
      * @method index_or_selected
      * @param {Number} index A cell's index
      * @return {Number} The given index, or selected index if none is provided.
      */
     Notebook.prototype.index_or_selected = function (index) {
         var i;
         if (index === undefined || index === null) {
             i = this.get_selected_index();
             if (i === null) {
                 i = 0;
             }
         } else {
             i = index;
         }
         return i;
     };
 
     /**
      * Get the currently selected cell.
      * @method get_selected_cell
      * @return {Cell} The selected cell
      */
     Notebook.prototype.get_selected_cell = function () {
         var index = this.get_selected_index();
         return this.get_cell(index);
     };
 
     /**
      * Check whether a cell index is valid.
      * 
      * @method is_valid_cell_index
      * @param {Number} index A cell index
      * @return True if the index is valid, false otherwise
      */
     Notebook.prototype.is_valid_cell_index = function (index) {
         if (index !== null && index >= 0 && index < this.ncells()) {
             return true;
         } else {
             return false;
         };
     }
 
     /**
      * Get the index of the currently selected cell.
      
      * @method get_selected_index
      * @return {Number} The selected cell's numeric index
      */
     Notebook.prototype.get_selected_index = function () {
         var result = null;
         this.get_cell_elements().filter(function (index) {
             if ($(this).data("cell").selected === true) {
                 result = index;
             };
         });
         return result;
     };
 
 
     // Cell selection.
 
     /**
      * Programmatically select a cell.
      * 
      * @method select
      * @param {Number} index A cell's index
      * @return {Notebook} This notebook
      */
     Notebook.prototype.select = function (index) {
         if (this.is_valid_cell_index(index)) {
             var sindex = this.get_selected_index()
             if (sindex !== null && index !== sindex) {
                 this.get_cell(sindex).unselect();
             };
             var cell = this.get_cell(index);
             cell.select();
             if (cell.cell_type === 'heading') {
                 $([IPython.events]).trigger('selected_cell_type_changed.Notebook',
                     {'cell_type':cell.cell_type,level:cell.level}
                 );
             } else {
                 $([IPython.events]).trigger('selected_cell_type_changed.Notebook',
                     {'cell_type':cell.cell_type}
                 );
             };
         };
         return this;
     };
 
     /**
      * Programmatically select the next cell.
      *
      * @method select_next
      * @return {Notebook} This notebook
      */
     Notebook.prototype.select_next = function () {
         var index = this.get_selected_index();
         this.select(index+1);
         return this;
     };
 
     /**
      * Programmatically select the previous cell.
      *
      * @method select_prev
      * @return {Notebook} This notebook
      */
     Notebook.prototype.select_prev = function () {
         var index = this.get_selected_index();
         this.select(index-1);
         return this;
     };
 
 
     // Cell movement
 
     /**
      * Move given (or selected) cell up and select it.
      * 
      * @method move_cell_up
      * @param [index] {integer} cell index
      * @return {Notebook} This notebook
      **/
     Notebook.prototype.move_cell_up = function (index) {
         var i = this.index_or_selected(index);
         if (this.is_valid_cell_index(i) && i > 0) {
             var pivot = this.get_cell_element(i-1);
             var tomove = this.get_cell_element(i);
             if (pivot !== null && tomove !== null) {
                 tomove.detach();
                 pivot.before(tomove);
                 this.select(i-1);
             };
             this.set_dirty(true);
         };
         return this;
     };
 
 
     /**
      * Move given (or selected) cell down and select it
      * 
      * @method move_cell_down
      * @param [index] {integer} cell index
      * @return {Notebook} This notebook
      **/
     Notebook.prototype.move_cell_down = function (index) {
         var i = this.index_or_selected(index);
         if ( this.is_valid_cell_index(i) && this.is_valid_cell_index(i+1)) {
             var pivot = this.get_cell_element(i+1);
             var tomove = this.get_cell_element(i);
             if (pivot !== null && tomove !== null) {
                 tomove.detach();
                 pivot.after(tomove);
                 this.select(i+1);
             };
         };
         this.set_dirty();
         return this;
     };
 
 
     // Insertion, deletion.
 
     /**
      * Delete a cell from the notebook.
      * 
      * @method delete_cell
      * @param [index] A cell's numeric index
      * @return {Notebook} This notebook
      */
     Notebook.prototype.delete_cell = function (index) {
         var i = this.index_or_selected(index);
         var cell = this.get_selected_cell();
         this.undelete_backup = cell.toJSON();
         $('#undelete_cell').removeClass('disabled');
         if (this.is_valid_cell_index(i)) {
             var ce = this.get_cell_element(i);
             ce.remove();
             if (i === (this.ncells())) {
                 this.select(i-1);
                 this.undelete_index = i - 1;
                 this.undelete_below = true;
             } else {
                 this.select(i);
                 this.undelete_index = i;
                 this.undelete_below = false;
             };
             $([IPython.events]).trigger('delete.Cell', {'cell': cell, 'index': i});
             this.set_dirty(true);
         };
         return this;
     };
 
     /**
      * Insert a cell so that after insertion the cell is at given index.
      *
      * Similar to insert_above, but index parameter is mandatory
      *
      * Index will be brought back into the accissible range [0,n]
      *
      * @method insert_cell_at_index
      * @param type {string} in ['code','markdown','heading']
      * @param [index] {int} a valid index where to inser cell
      *
      * @return cell {cell|null} created cell or null
      **/
     Notebook.prototype.insert_cell_at_index = function(type, index){
 
         var ncells = this.ncells();
         var index = Math.min(index,ncells);
             index = Math.max(index,0);
         var cell = null;
 
         if (ncells === 0 || this.is_valid_cell_index(index) || index === ncells) {
             if (type === 'code') {
                 cell = new IPython.CodeCell(this.kernel);
                 cell.set_input_prompt();
             } else if (type === 'markdown') {
                 cell = new IPython.MarkdownCell();
             } else if (type === 'raw') {
                 cell = new IPython.RawCell();
             } else if (type === 'heading') {
                 cell = new IPython.HeadingCell();
             }
 
             if(this._insert_element_at_index(cell.element,index)){
                 cell.render();
                 this.select(this.find_cell_index(cell));
                 $([IPython.events]).trigger('create.Cell', {'cell': cell, 'index': index});
                 this.set_dirty(true);
             }
         }
         return cell;
 
     };
 
     /**
      * Insert an element at given cell index.
      *
      * @method _insert_element_at_index
      * @param element {dom element} a cell element
      * @param [index] {int} a valid index where to inser cell
      * @private
      *
      * return true if everything whent fine.
      **/
     Notebook.prototype._insert_element_at_index = function(element, index){
         if (element === undefined){
             return false;
         }
 
         var ncells = this.ncells();
 
         if (ncells === 0) {
             // special case append if empty
             this.element.find('div.end_space').before(element);
         } else if ( ncells === index ) {
             // special case append it the end, but not empty
             this.get_cell_element(index-1).after(element);
         } else if (this.is_valid_cell_index(index)) {
             // otherwise always somewhere to append to
             this.get_cell_element(index).before(element);
         } else {
             return false;
         }
 
         if (this.undelete_index !== null && index <= this.undelete_index) {
             this.undelete_index = this.undelete_index + 1;
             this.set_dirty(true);
         }
         return true;
     };
 
     /**
      * Insert a cell of given type above given index, or at top
      * of notebook if index smaller than 0.
      *
      * default index value is the one of currently selected cell
      *
      * @method insert_cell_above
      * @param type {string} cell type
      * @param [index] {integer}
      *
      * @return handle to created cell or null
      **/
     Notebook.prototype.insert_cell_above = function (type, index) {
         index = this.index_or_selected(index);
         return this.insert_cell_at_index(type, index);
     };
 
     /**
      * Insert a cell of given type below given index, or at bottom
      * of notebook if index greater thatn number of cell
      *
      * default index value is the one of currently selected cell
      *
      * @method insert_cell_below
      * @param type {string} cell type
      * @param [index] {integer}
      *
      * @return handle to created cell or null
      *
      **/
     Notebook.prototype.insert_cell_below = function (type, index) {
         index = this.index_or_selected(index);
         return this.insert_cell_at_index(type, index+1);
     };
 
 
     /**
      * Insert cell at end of notebook
      *
      * @method insert_cell_at_bottom
      * @param {String} type cell type
      *
      * @return the added cell; or null
      **/
     Notebook.prototype.insert_cell_at_bottom = function (type){
         var len = this.ncells();
         return this.insert_cell_below(type,len-1);
     };
 
     /**
      * Turn a cell into a code cell.
      * 
      * @method to_code
      * @param {Number} [index] A cell's index
      */
     Notebook.prototype.to_code = function (index) {
         var i = this.index_or_selected(index);
         if (this.is_valid_cell_index(i)) {
             var source_element = this.get_cell_element(i);
             var source_cell = source_element.data("cell");
             if (!(source_cell instanceof IPython.CodeCell)) {
                 var target_cell = this.insert_cell_below('code',i);
                 var text = source_cell.get_text();
                 if (text === source_cell.placeholder) {
                     text = '';
                 }
                 target_cell.set_text(text);
                 // make this value the starting point, so that we can only undo
                 // to this state, instead of a blank cell
                 target_cell.code_mirror.clearHistory();
                 source_element.remove();
                 this.set_dirty(true);
             };
         };
     };
 
     /**
      * Turn a cell into a Markdown cell.
      * 
      * @method to_markdown
      * @param {Number} [index] A cell's index
      */
     Notebook.prototype.to_markdown = function (index) {
         var i = this.index_or_selected(index);
         if (this.is_valid_cell_index(i)) {
             var source_element = this.get_cell_element(i);
             var source_cell = source_element.data("cell");
             if (!(source_cell instanceof IPython.MarkdownCell)) {
                 var target_cell = this.insert_cell_below('markdown',i);
                 var text = source_cell.get_text();
                 if (text === source_cell.placeholder) {
                     text = '';
                 };
                 // The edit must come before the set_text.
                 target_cell.edit();
                 target_cell.set_text(text);
                 // make this value the starting point, so that we can only undo
                 // to this state, instead of a blank cell
                 target_cell.code_mirror.clearHistory();
                 source_element.remove();
                 this.set_dirty(true);
             };
         };
     };
 
     /**
      * Turn a cell into a raw text cell.
      * 
      * @method to_raw
      * @param {Number} [index] A cell's index
      */
     Notebook.prototype.to_raw = function (index) {
         var i = this.index_or_selected(index);
         if (this.is_valid_cell_index(i)) {
             var source_element = this.get_cell_element(i);
             var source_cell = source_element.data("cell");
             var target_cell = null;
             if (!(source_cell instanceof IPython.RawCell)) {
                 target_cell = this.insert_cell_below('raw',i);
                 var text = source_cell.get_text();
                 if (text === source_cell.placeholder) {
                     text = '';
                 };
                 // The edit must come before the set_text.
                 target_cell.edit();
                 target_cell.set_text(text);
                 // make this value the starting point, so that we can only undo
                 // to this state, instead of a blank cell
                 target_cell.code_mirror.clearHistory();
                 source_element.remove();
                 this.set_dirty(true);
             };
         };
     };
 
     /**
      * Turn a cell into a heading cell.
      * 
      * @method to_heading
      * @param {Number} [index] A cell's index
      * @param {Number} [level] A heading level (e.g., 1 becomes &lt;h1&gt;)
      */
     Notebook.prototype.to_heading = function (index, level) {
         level = level || 1;
         var i = this.index_or_selected(index);
         if (this.is_valid_cell_index(i)) {
             var source_element = this.get_cell_element(i);
             var source_cell = source_element.data("cell");
             var target_cell = null;
             if (source_cell instanceof IPython.HeadingCell) {
                 source_cell.set_level(level);
             } else {
                 target_cell = this.insert_cell_below('heading',i);
                 var text = source_cell.get_text();
                 if (text === source_cell.placeholder) {
                     text = '';
                 };
                 // The edit must come before the set_text.
                 target_cell.set_level(level);
                 target_cell.edit();
                 target_cell.set_text(text);
                 // make this value the starting point, so that we can only undo
                 // to this state, instead of a blank cell
                 target_cell.code_mirror.clearHistory();
                 source_element.remove();
                 this.set_dirty(true);
             };
             $([IPython.events]).trigger('selected_cell_type_changed.Notebook',
                 {'cell_type':'heading',level:level}
             );
         };
     };
 
 
     // Cut/Copy/Paste
 
     /**
      * Enable UI elements for pasting cells.
      * 
      * @method enable_paste
      */
     Notebook.prototype.enable_paste = function () {
         var that = this;
         if (!this.paste_enabled) {
             $('#paste_cell_replace').removeClass('disabled')
                 .on('click', function () {that.paste_cell_replace();});
             $('#paste_cell_above').removeClass('disabled')
                 .on('click', function () {that.paste_cell_above();});
             $('#paste_cell_below').removeClass('disabled')
                 .on('click', function () {that.paste_cell_below();});
             this.paste_enabled = true;
         };
     };
 
     /**
      * Disable UI elements for pasting cells.
      * 
      * @method disable_paste
      */
     Notebook.prototype.disable_paste = function () {
         if (this.paste_enabled) {
             $('#paste_cell_replace').addClass('disabled').off('click');
             $('#paste_cell_above').addClass('disabled').off('click');
             $('#paste_cell_below').addClass('disabled').off('click');
             this.paste_enabled = false;
         };
     };
 
     /**
      * Cut a cell.
      * 
      * @method cut_cell
      */
     Notebook.prototype.cut_cell = function () {
         this.copy_cell();
         this.delete_cell();
     }
 
     /**
      * Copy a cell.
      * 
      * @method copy_cell
      */
     Notebook.prototype.copy_cell = function () {
         var cell = this.get_selected_cell();
         this.clipboard = cell.toJSON();
         this.enable_paste();
     };
 
     /**
      * Replace the selected cell with a cell in the clipboard.
      * 
      * @method paste_cell_replace
      */
     Notebook.prototype.paste_cell_replace = function () {
         if (this.clipboard !== null && this.paste_enabled) {
             var cell_data = this.clipboard;
             var new_cell = this.insert_cell_above(cell_data.cell_type);
             new_cell.fromJSON(cell_data);
             var old_cell = this.get_next_cell(new_cell);
             this.delete_cell(this.find_cell_index(old_cell));
             this.select(this.find_cell_index(new_cell));
         };
     };
 
     /**
      * Paste a cell from the clipboard above the selected cell.
      * 
      * @method paste_cell_above
      */
     Notebook.prototype.paste_cell_above = function () {
         if (this.clipboard !== null && this.paste_enabled) {
             var cell_data = this.clipboard;
             var new_cell = this.insert_cell_above(cell_data.cell_type);
             new_cell.fromJSON(cell_data);
         };
     };
 
     /**
      * Paste a cell from the clipboard below the selected cell.
      * 
      * @method paste_cell_below
      */
     Notebook.prototype.paste_cell_below = function () {
         if (this.clipboard !== null && this.paste_enabled) {
             var cell_data = this.clipboard;
             var new_cell = this.insert_cell_below(cell_data.cell_type);
             new_cell.fromJSON(cell_data);
         };
     };
 
     // Cell undelete
 
     /**
      * Restore the most recently deleted cell.
      * 
      * @method undelete
      */
     Notebook.prototype.undelete = function() {
         if (this.undelete_backup !== null && this.undelete_index !== null) {
             var current_index = this.get_selected_index();
             if (this.undelete_index < current_index) {
                 current_index = current_index + 1;
             }
             if (this.undelete_index >= this.ncells()) {
                 this.select(this.ncells() - 1);
             }
             else {
                 this.select(this.undelete_index);
             }
             var cell_data = this.undelete_backup;
             var new_cell = null;
             if (this.undelete_below) {
                 new_cell = this.insert_cell_below(cell_data.cell_type);
             } else {
                 new_cell = this.insert_cell_above(cell_data.cell_type);
             }
             new_cell.fromJSON(cell_data);
             this.select(current_index);
             this.undelete_backup = null;
             this.undelete_index = null;
         }
         $('#undelete_cell').addClass('disabled');
     }
 
     // Split/merge
 
     /**
      * Split the selected cell into two, at the cursor.
      * 
      * @method split_cell
      */
     Notebook.prototype.split_cell = function () {
         // Todo: implement spliting for other cell types.
         var cell = this.get_selected_cell();
         if (cell.is_splittable()) {
             var texta = cell.get_pre_cursor();
             var textb = cell.get_post_cursor();
             if (cell instanceof IPython.CodeCell) {
                 cell.set_text(texta);
                 var new_cell = this.insert_cell_below('code');
                 new_cell.set_text(textb);
             } else if (cell instanceof IPython.MarkdownCell) {
                 cell.set_text(texta);
                 cell.render();
                 var new_cell = this.insert_cell_below('markdown');
                 new_cell.edit(); // editor must be visible to call set_text
                 new_cell.set_text(textb);
                 new_cell.render();
             }
         };
     };
 
     /**
      * Combine the selected cell into the cell above it.
      * 
      * @method merge_cell_above
      */
     Notebook.prototype.merge_cell_above = function () {
         var index = this.get_selected_index();
         var cell = this.get_cell(index);
         if (index > 0) {
             var upper_cell = this.get_cell(index-1);
             var upper_text = upper_cell.get_text();
             var text = cell.get_text();
             if (cell instanceof IPython.CodeCell) {
                 cell.set_text(upper_text+'\n'+text);
             } else if (cell instanceof IPython.MarkdownCell) {
                 cell.edit();
                 cell.set_text(upper_text+'\n'+text);
                 cell.render();
             };
             this.delete_cell(index-1);
             this.select(this.find_cell_index(cell));
         };
     };
 
     /**
      * Combine the selected cell into the cell below it.
      * 
      * @method merge_cell_below
      */
     Notebook.prototype.merge_cell_below = function () {
         var index = this.get_selected_index();
         var cell = this.get_cell(index);
         if (index < this.ncells()-1) {
             var lower_cell = this.get_cell(index+1);
             var lower_text = lower_cell.get_text();
             var text = cell.get_text();
             if (cell instanceof IPython.CodeCell) {
                 cell.set_text(text+'\n'+lower_text);
             } else if (cell instanceof IPython.MarkdownCell) {
                 cell.edit();
                 cell.set_text(text+'\n'+lower_text);
                 cell.render();
             };
             this.delete_cell(index+1);
             this.select(this.find_cell_index(cell));
         };
     };
 
 
     // Cell collapsing and output clearing
 
     /**
      * Hide a cell's output.
      * 
      * @method collapse
      * @param {Number} index A cell's numeric index
      */
     Notebook.prototype.collapse = function (index) {
         var i = this.index_or_selected(index);
         this.get_cell(i).collapse();
         this.set_dirty(true);
     };
 
     /**
      * Show a cell's output.
      * 
      * @method expand
      * @param {Number} index A cell's numeric index
      */
     Notebook.prototype.expand = function (index) {
         var i = this.index_or_selected(index);
         this.get_cell(i).expand();
         this.set_dirty(true);
     };
 
     /** Toggle whether a cell's output is collapsed or expanded.
      * 
      * @method toggle_output
      * @param {Number} index A cell's numeric index
      */
     Notebook.prototype.toggle_output = function (index) {
         var i = this.index_or_selected(index);
         this.get_cell(i).toggle_output();
         this.set_dirty(true);
     };
 
     /**
      * Toggle a scrollbar for long cell outputs.
      * 
      * @method toggle_output_scroll
      * @param {Number} index A cell's numeric index
      */
     Notebook.prototype.toggle_output_scroll = function (index) {
         var i = this.index_or_selected(index);
         this.get_cell(i).toggle_output_scroll();
     };
 
     /**
      * Hide each code cell's output area.
      * 
      * @method collapse_all_output
      */
     Notebook.prototype.collapse_all_output = function () {
         var ncells = this.ncells();
         var cells = this.get_cells();
         for (var i=0; i<ncells; i++) {
             if (cells[i] instanceof IPython.CodeCell) {
                 cells[i].output_area.collapse();
             }
         };
         // this should not be set if the `collapse` key is removed from nbformat
         this.set_dirty(true);
     };
 
     /**
      * Expand each code cell's output area, and add a scrollbar for long output.
      * 
      * @method scroll_all_output
      */
     Notebook.prototype.scroll_all_output = function () {
         var ncells = this.ncells();
         var cells = this.get_cells();
         for (var i=0; i<ncells; i++) {
             if (cells[i] instanceof IPython.CodeCell) {
                 cells[i].output_area.expand();
                 cells[i].output_area.scroll_if_long();
             }
         };
         // this should not be set if the `collapse` key is removed from nbformat
         this.set_dirty(true);
     };
 
     /**
      * Expand each code cell's output area, and remove scrollbars.
      * 
      * @method expand_all_output
      */
     Notebook.prototype.expand_all_output = function () {
         var ncells = this.ncells();
         var cells = this.get_cells();
         for (var i=0; i<ncells; i++) {
             if (cells[i] instanceof IPython.CodeCell) {
                 cells[i].output_area.expand();
                 cells[i].output_area.unscroll_area();
             }
         };
         // this should not be set if the `collapse` key is removed from nbformat
         this.set_dirty(true);
     };
 
     /**
      * Clear each code cell's output area.
      * 
      * @method clear_all_output
      */
     Notebook.prototype.clear_all_output = function () {
         var ncells = this.ncells();
         var cells = this.get_cells();
         for (var i=0; i<ncells; i++) {
             if (cells[i] instanceof IPython.CodeCell) {
                 cells[i].clear_output(true,true,true);
                 // Make all In[] prompts blank, as well
                 // TODO: make this configurable (via checkbox?)
                 cells[i].set_input_prompt();
             }
         };
         this.set_dirty(true);
     };
 
 
     // Other cell functions: line numbers, ...
 
     /**
      * Toggle line numbers in the selected cell's input area.
      * 
      * @method cell_toggle_line_numbers
      */
     Notebook.prototype.cell_toggle_line_numbers = function() {
         this.get_selected_cell().toggle_line_numbers();
     };
 
     // Kernel related things
 
     /**
      * Start a new kernel and set it on each code cell.
      * 
      * @method start_kernel
      */
     Notebook.prototype.start_kernel = function () {
         var base_url = $('body').data('baseKernelUrl') + "kernels";
         this.kernel = new IPython.Kernel(base_url);
         this.kernel.start(this.notebook_id);
         // Now that the kernel has been created, tell the CodeCells about it.
         var ncells = this.ncells();
         for (var i=0; i<ncells; i++) {
             var cell = this.get_cell(i);
             if (cell instanceof IPython.CodeCell) {
                 cell.set_kernel(this.kernel)
             };
         };
     };
 
     /**
      * Prompt the user to restart the IPython kernel.
      * 
      * @method restart_kernel
      */
     Notebook.prototype.restart_kernel = function () {
         var that = this;
         IPython.dialog.modal({
             title : "Restart kernel or continue running?",
             body : $("<p/>").html(
                 'Do you want to restart the current kernel?  You will lose all variables defined in it.'
             ),
             buttons : {
                 "Continue running" : {},
                 "Restart" : {
                     "class" : "btn-danger",
                     "click" : function() {
                         that.kernel.restart();
                     }
                 }
             }
         });
     };
 
     /**
      * Run the selected cell.
      * 
      * Execute or render cell outputs.
      * 
      * @method execute_selected_cell
      * @param {Object} options Customize post-execution behavior
      */
     Notebook.prototype.execute_selected_cell = function (options) {
         // add_new: should a new cell be added if we are at the end of the nb
         // terminal: execute in terminal mode, which stays in the current cell
         var default_options = {terminal: false, add_new: true};
         $.extend(default_options, options);
         var that = this;
         var cell = that.get_selected_cell();
         var cell_index = that.find_cell_index(cell);
         if (cell instanceof IPython.CodeCell) {
             cell.execute();
         }
         if (default_options.terminal) {
             cell.select_all();
         } else {
             if ((cell_index === (that.ncells()-1)) && default_options.add_new) {
                 that.insert_cell_below('code');
                 // If we are adding a new cell at the end, scroll down to show it.
                 that.scroll_to_bottom();
             } else {
                 that.select(cell_index+1);
             };
         };
         this.set_dirty(true);
     };
 
     /**
      * Execute all cells below the selected cell.
      * 
      * @method execute_cells_below
      */
     Notebook.prototype.execute_cells_below = function () {
         this.execute_cell_range(this.get_selected_index(), this.ncells());
         this.scroll_to_bottom();
     };
 
     /**
      * Execute all cells above the selected cell.
      * 
      * @method execute_cells_above
      */
     Notebook.prototype.execute_cells_above = function () {
         this.execute_cell_range(0, this.get_selected_index());
     };
 
     /**
      * Execute all cells.
      * 
      * @method execute_all_cells
      */
     Notebook.prototype.execute_all_cells = function () {
         this.execute_cell_range(0, this.ncells());
         this.scroll_to_bottom();
     };
 
     /**
      * Execute a contiguous range of cells.
      * 
      * @method execute_cell_range
      * @param {Number} start Index of the first cell to execute (inclusive)
      * @param {Number} end Index of the last cell to execute (exclusive)
      */
     Notebook.prototype.execute_cell_range = function (start, end) {
         for (var i=start; i<end; i++) {
             this.select(i);
             this.execute_selected_cell({add_new:false});
         };
     };
 
     // Persistance and loading
 
     /**
      * Getter method for this notebook's ID.
      * 
      * @method get_notebook_id
      * @return {String} This notebook's ID
      */
     Notebook.prototype.get_notebook_id = function () {
         return this.notebook_id;
     };
 
     /**
      * Getter method for this notebook's name.
      * 
      * @method get_notebook_name
      * @return {String} This notebook's name
      */
     Notebook.prototype.get_notebook_name = function () {
         return this.notebook_name;
     };
 
     /**
      * Setter method for this notebook's name.
      *
      * @method set_notebook_name
      * @param {String} name A new name for this notebook
      */
     Notebook.prototype.set_notebook_name = function (name) {
         this.notebook_name = name;
     };
 
     /**
      * Check that a notebook's name is valid.
      * 
      * @method test_notebook_name
      * @param {String} nbname A name for this notebook
      * @return {Boolean} True if the name is valid, false if invalid
      */
     Notebook.prototype.test_notebook_name = function (nbname) {
         nbname = nbname || '';
         if (this.notebook_name_blacklist_re.test(nbname) == false && nbname.length>0) {
             return true;
         } else {
             return false;
         };
     };
 
     /**
      * Load a notebook from JSON (.ipynb).
      * 
      * This currently handles one worksheet: others are deleted.
      * 
      * @method fromJSON
      * @param {Object} data JSON representation of a notebook
      */
     Notebook.prototype.fromJSON = function (data) {
         var ncells = this.ncells();
         var i;
         for (i=0; i<ncells; i++) {
             // Always delete cell 0 as they get renumbered as they are deleted.
             this.delete_cell(0);
         };
         // Save the metadata and name.
         this.metadata = data.metadata;
         this.notebook_name = data.metadata.name;
         // Only handle 1 worksheet for now.
         var worksheet = data.worksheets[0];
         if (worksheet !== undefined) {
             if (worksheet.metadata) {
                 this.worksheet_metadata = worksheet.metadata;
             }
             var new_cells = worksheet.cells;
             ncells = new_cells.length;
             var cell_data = null;
             var new_cell = null;
             for (i=0; i<ncells; i++) {
                 cell_data = new_cells[i];
                 // VERSIONHACK: plaintext -> raw
                 // handle never-released plaintext name for raw cells
                 if (cell_data.cell_type === 'plaintext'){
                     cell_data.cell_type = 'raw';
                 }
 
                 new_cell = this.insert_cell_below(cell_data.cell_type);
                 new_cell.fromJSON(cell_data);
             };
         };
         if (data.worksheets.length > 1) {
             IPython.dialog.modal({
                 title : "Multiple worksheets",
                 body : "This notebook has " + data.worksheets.length + " worksheets, " +
                     "but this version of IPython can only handle the first.  " +
                     "If you save this notebook, worksheets after the first will be lost.",
                 buttons : {
                     OK : {
                         class : "btn-danger"
                     }
                 }
             });
         }
     };
 
     /**
      * Dump this notebook into a JSON-friendly object.
      * 
      * @method toJSON
      * @return {Object} A JSON-friendly representation of this notebook.
      */
     Notebook.prototype.toJSON = function () {
         var cells = this.get_cells();
         var ncells = cells.length;
         var cell_array = new Array(ncells);
         for (var i=0; i<ncells; i++) {
             cell_array[i] = cells[i].toJSON();
         };
         var data = {
             // Only handle 1 worksheet for now.
             worksheets : [{
                 cells: cell_array,
                 metadata: this.worksheet_metadata
             }],
             metadata : this.metadata
         };
         return data;
     };
 
     /**
      * Start an autosave timer, for periodically saving the notebook.
      * 
      * @method set_autosave_interval
      * @param {Integer} interval the autosave interval in milliseconds
      */
     Notebook.prototype.set_autosave_interval = function (interval) {
         var that = this;
         // clear previous interval, so we don't get simultaneous timers
         if (this.autosave_timer) {
             clearInterval(this.autosave_timer);
         }
         
         this.autosave_interval = this.minimum_autosave_interval = interval;
         if (interval) {
             this.autosave_timer = setInterval(function() {
                 if (that.dirty) {
                     that.save_notebook();
                 }
             }, interval);
             $([IPython.events]).trigger("autosave_enabled.Notebook", interval);
         } else {
             this.autosave_timer = null;
             $([IPython.events]).trigger("autosave_disabled.Notebook");
         };
     };
     
     /**
      * Save this notebook on the server.
      * 
      * @method save_notebook
      */
     Notebook.prototype.save_notebook = function () {
         // We may want to move the name/id/nbformat logic inside toJSON?
         var data = this.toJSON();
         data.metadata.name = this.notebook_name;
         data.nbformat = this.nbformat;
         data.nbformat_minor = this.nbformat_minor;
         
         // time the ajax call for autosave tuning purposes.
         var start =  new Date().getTime();
 
         // We do the call with settings so we can set cache to false.
         var settings = {
             processData : false,
             cache : false,
             type : "PUT",
             data : JSON.stringify(data),
             headers : {'Content-Type': 'application/json'},
             success : $.proxy(this.save_notebook_success, this, start),
             error : $.proxy(this.save_notebook_error, this)
         };
         $([IPython.events]).trigger('notebook_saving.Notebook');
         var url = this.baseProjectUrl() + 'notebooks/' + this.notebook_id;
         $.ajax(url, settings);
     };
     
     /**
      * Success callback for saving a notebook.
      * 
      * @method save_notebook_success
      * @param {Integer} start the time when the save request started
      * @param {Object} data JSON representation of a notebook
      * @param {String} status Description of response status
      * @param {jqXHR} xhr jQuery Ajax object
      */
     Notebook.prototype.save_notebook_success = function (start, data, status, xhr) {
         this.set_dirty(false);
         $([IPython.events]).trigger('notebook_saved.Notebook');
         this._update_autosave_interval(start);
         if (this._checkpoint_after_save) {
             this.create_checkpoint();
             this._checkpoint_after_save = false;
         };
     };
     
     /**
      * update the autosave interval based on how long the last save took
      * 
      * @method _update_autosave_interval
      * @param {Integer} timestamp when the save request started
      */
     Notebook.prototype._update_autosave_interval = function (start) {
         var duration = (new Date().getTime() - start);
         if (this.autosave_interval) {
             // new save interval: higher of 10x save duration or parameter (default 30 seconds)
             var interval = Math.max(10 * duration, this.minimum_autosave_interval);
             // round to 10 seconds, otherwise we will be setting a new interval too often
             interval = 10000 * Math.round(interval / 10000);
             // set new interval, if it's changed
             if (interval != this.autosave_interval) {
                 this.set_autosave_interval(interval);
             }
         }
     };
     
     /**
      * Failure callback for saving a notebook.
      * 
      * @method save_notebook_error
      * @param {jqXHR} xhr jQuery Ajax object
      * @param {String} status Description of response status
      * @param {String} error_msg HTTP error message
      */
     Notebook.prototype.save_notebook_error = function (xhr, status, error_msg) {
         $([IPython.events]).trigger('notebook_save_failed.Notebook');
     };
     
     /**
      * Request a notebook's data from the server.
      * 
      * @method load_notebook
      * @param {String} notebook_id A notebook to load
      */
     Notebook.prototype.load_notebook = function (notebook_id) {
         var that = this;
         this.notebook_id = notebook_id;
         // We do the call with settings so we can set cache to false.
         var settings = {
             processData : false,
             cache : false,
             type : "GET",
             dataType : "json",
             success : $.proxy(this.load_notebook_success,this),
             error : $.proxy(this.load_notebook_error,this),
         };
         $([IPython.events]).trigger('notebook_loading.Notebook');
         var url = this.baseProjectUrl() + 'notebooks/' + this.notebook_id;
         $.ajax(url, settings);
     };
 
     /**
      * Success callback for loading a notebook from the server.
      * 
      * Load notebook data from the JSON response.
      * 
      * @method load_notebook_success
      * @param {Object} data JSON representation of a notebook
      * @param {String} status Description of response status
      * @param {jqXHR} xhr jQuery Ajax object
      */
     Notebook.prototype.load_notebook_success = function (data, status, xhr) {
         this.fromJSON(data);
         if (this.ncells() === 0) {
             this.insert_cell_below('code');
         };
         this.set_dirty(false);
         this.select(0);
         this.scroll_to_top();
         if (data.orig_nbformat !== undefined && data.nbformat !== data.orig_nbformat) {
             var msg = "This notebook has been converted from an older " +
             "notebook format (v"+data.orig_nbformat+") to the current notebook " +
             "format (v"+data.nbformat+"). The next time you save this notebook, the " +
             "newer notebook format will be used and older versions of IPython " +
             "may not be able to read it. To keep the older version, close the " +
             "notebook without saving it.";
             IPython.dialog.modal({
                 title : "Notebook converted",
                 body : msg,
                 buttons : {
                     OK : {
                         class : "btn-primary"
                     }
                 }
             });
         } else if (data.orig_nbformat_minor !== undefined && data.nbformat_minor !== data.orig_nbformat_minor) {
             var that = this;
             var orig_vs = 'v' + data.nbformat + '.' + data.orig_nbformat_minor;
             var this_vs = 'v' + data.nbformat + '.' + this.nbformat_minor;
             var msg = "This notebook is version " + orig_vs + ", but we only fully support up to " +
             this_vs + ".  You can still work with this notebook, but some features " +
             "introduced in later notebook versions may not be available."
 
             IPython.dialog.modal({
                 title : "Newer Notebook",
                 body : msg,
                 buttons : {
                     OK : {
                         class : "btn-danger"
                     }
                 }
             });
 
         }
         
         // Create the kernel after the notebook is completely loaded to prevent
         // code execution upon loading, which is a security risk.
         if (! this.read_only) {
             this.start_kernel();
             // load our checkpoint list
             IPython.notebook.list_checkpoints();
         }
         $([IPython.events]).trigger('notebook_loaded.Notebook');
     };
 
     /**
      * Failure callback for loading a notebook from the server.
      * 
      * @method load_notebook_error
      * @param {jqXHR} xhr jQuery Ajax object
      * @param {String} textStatus Description of response status
      * @param {String} errorThrow HTTP error message
      */
     Notebook.prototype.load_notebook_error = function (xhr, textStatus, errorThrow) {
-        if (xhr.status === 500) {
-            var msg = "An error occurred while loading this notebook. Most likely " +
-            "this notebook is in a newer format than is supported by this " +
-            "version of IPython. This version can load notebook formats " +
-            "v"+this.nbformat+" or earlier.";
-            
-            IPython.dialog.modal({
-                title: "Error loading notebook",
-                body : msg,
-                buttons : {
-                    "OK": {}
-                }
-            });
+        if (xhr.status === 400) {
+            var msg = errorThrow;
+        } else if (xhr.status === 500) {
+            var msg = "An unknown error occurred while loading this notebook. " +
+            "This version can load notebook formats " +
+            "v" + this.nbformat + " or earlier.";
         }
+        IPython.dialog.modal({
+            title: "Error loading notebook",
+            body : msg,
+            buttons : {
+                "OK": {}
+            }
+        });
     }
 
     /*********************  checkpoint-related  *********************/
     
     /**
      * Save the notebook then immediately create a checkpoint.
      * 
      * @method save_checkpoint
      */
     Notebook.prototype.save_checkpoint = function () {
         this._checkpoint_after_save = true;
         this.save_notebook();
     };
     
     /**
      * List checkpoints for this notebook.
      * 
      * @method list_checkpoint
      */
     Notebook.prototype.list_checkpoints = function () {
         var url = this.baseProjectUrl() + 'notebooks/' + this.notebook_id + '/checkpoints';
         $.get(url).done(
             $.proxy(this.list_checkpoints_success, this)
         ).fail(
             $.proxy(this.list_checkpoints_error, this)
         );
     };
 
     /**
      * Success callback for listing checkpoints.
      * 
      * @method list_checkpoint_success
      * @param {Object} data JSON representation of a checkpoint
      * @param {String} status Description of response status
      * @param {jqXHR} xhr jQuery Ajax object
      */
     Notebook.prototype.list_checkpoints_success = function (data, status, xhr) {
         var data = $.parseJSON(data);
         if (data.length) {
             this.last_checkpoint = data[0];
         } else {
             this.last_checkpoint = null;
         }
         $([IPython.events]).trigger('checkpoints_listed.Notebook', [data]);
     };
 
     /**
      * Failure callback for listing a checkpoint.
      * 
      * @method list_checkpoint_error
      * @param {jqXHR} xhr jQuery Ajax object
      * @param {String} status Description of response status
      * @param {String} error_msg HTTP error message
      */
     Notebook.prototype.list_checkpoints_error = function (xhr, status, error_msg) {
         $([IPython.events]).trigger('list_checkpoints_failed.Notebook');
     };
     
     /**
      * Create a checkpoint of this notebook on the server from the most recent save.
      * 
      * @method create_checkpoint
      */
     Notebook.prototype.create_checkpoint = function () {
         var url = this.baseProjectUrl() + 'notebooks/' + this.notebook_id + '/checkpoints';
         $.post(url).done(
             $.proxy(this.create_checkpoint_success, this)
         ).fail(
             $.proxy(this.create_checkpoint_error, this)
         );
     };
 
     /**
      * Success callback for creating a checkpoint.
      * 
      * @method create_checkpoint_success
      * @param {Object} data JSON representation of a checkpoint
      * @param {String} status Description of response status
      * @param {jqXHR} xhr jQuery Ajax object
      */
     Notebook.prototype.create_checkpoint_success = function (data, status, xhr) {
         var data = $.parseJSON(data);
         this.last_checkpoint = data;
         $([IPython.events]).trigger('checkpoint_created.Notebook', data);
     };
 
     /**
      * Failure callback for creating a checkpoint.
      * 
      * @method create_checkpoint_error
      * @param {jqXHR} xhr jQuery Ajax object
      * @param {String} status Description of response status
      * @param {String} error_msg HTTP error message
      */
     Notebook.prototype.create_checkpoint_error = function (xhr, status, error_msg) {
         $([IPython.events]).trigger('checkpoint_failed.Notebook');
     };
     
     Notebook.prototype.restore_checkpoint_dialog = function (checkpoint) {
         var that = this;
         var checkpoint = checkpoint || this.last_checkpoint;
         if ( ! checkpoint ) {
             console.log("restore dialog, but no checkpoint to restore to!");
             return;
         }
         var body = $('<div/>').append(
             $('<p/>').addClass("p-space").text(
                 "Are you sure you want to revert the notebook to " +
                 "the latest checkpoint?"
             ).append(
                 $("<strong/>").text(
                     " This cannot be undone."
                 )
             )
         ).append(
             $('<p/>').addClass("p-space").text("The checkpoint was last updated at:")
         ).append(
             $('<p/>').addClass("p-space").text(
                 Date(checkpoint.last_modified)
             ).css("text-align", "center")
         );
         
         IPython.dialog.modal({
             title : "Revert notebook to checkpoint",
             body : body,
             buttons : {
                 Revert : {
                     class : "btn-danger",
                     click : function () {
                         that.restore_checkpoint(checkpoint.checkpoint_id);
                     }
                 },
                 Cancel : {}
                 }
         });
     }
     
     /**
      * Restore the notebook to a checkpoint state.
      * 
      * @method restore_checkpoint
      * @param {String} checkpoint ID
      */
     Notebook.prototype.restore_checkpoint = function (checkpoint) {
         $([IPython.events]).trigger('checkpoint_restoring.Notebook', checkpoint);
         var url = this.baseProjectUrl() + 'notebooks/' + this.notebook_id + '/checkpoints/' + checkpoint;
         $.post(url).done(
             $.proxy(this.restore_checkpoint_success, this)
         ).fail(
             $.proxy(this.restore_checkpoint_error, this)
         );
     };
     
     /**
      * Success callback for restoring a notebook to a checkpoint.
      * 
      * @method restore_checkpoint_success
      * @param {Object} data (ignored, should be empty)
      * @param {String} status Description of response status
      * @param {jqXHR} xhr jQuery Ajax object
      */
     Notebook.prototype.restore_checkpoint_success = function (data, status, xhr) {
         $([IPython.events]).trigger('checkpoint_restored.Notebook');
         this.load_notebook(this.notebook_id);
     };
 
     /**
      * Failure callback for restoring a notebook to a checkpoint.
      * 
      * @method restore_checkpoint_error
      * @param {jqXHR} xhr jQuery Ajax object
      * @param {String} status Description of response status
      * @param {String} error_msg HTTP error message
      */
     Notebook.prototype.restore_checkpoint_error = function (xhr, status, error_msg) {
         $([IPython.events]).trigger('checkpoint_restore_failed.Notebook');
     };
     
     /**
      * Delete a notebook checkpoint.
      * 
      * @method delete_checkpoint
      * @param {String} checkpoint ID
      */
     Notebook.prototype.delete_checkpoint = function (checkpoint) {
         $([IPython.events]).trigger('checkpoint_deleting.Notebook', checkpoint);
         var url = this.baseProjectUrl() + 'notebooks/' + this.notebook_id + '/checkpoints/' + checkpoint;
         $.ajax(url, {
             type: 'DELETE',
             success: $.proxy(this.delete_checkpoint_success, this),
             error: $.proxy(this.delete_notebook_error,this)
         });
     };
     
     /**
      * Success callback for deleting a notebook checkpoint
      * 
      * @method delete_checkpoint_success
      * @param {Object} data (ignored, should be empty)
      * @param {String} status Description of response status
      * @param {jqXHR} xhr jQuery Ajax object
      */
     Notebook.prototype.delete_checkpoint_success = function (data, status, xhr) {
         $([IPython.events]).trigger('checkpoint_deleted.Notebook', data);
         this.load_notebook(this.notebook_id);
     };
 
     /**
      * Failure callback for deleting a notebook checkpoint.
      * 
      * @method delete_checkpoint_error
      * @param {jqXHR} xhr jQuery Ajax object
      * @param {String} status Description of response status
      * @param {String} error_msg HTTP error message
      */
     Notebook.prototype.delete_checkpoint_error = function (xhr, status, error_msg) {
         $([IPython.events]).trigger('checkpoint_delete_failed.Notebook');
     };
 
 
     IPython.Notebook = Notebook;
 
 
     return IPython;
 
 }(IPython));
 

IPython/nbformat/current.py

@@ -1,221 +1,226 b''
 """The official API for working with notebooks in the current format version.
 
 Authors:
 
 * Brian Granger
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 from __future__ import print_function
 import json
 from xml.etree import ElementTree as ET
 import re
 
 from IPython.nbformat import v3
 from IPython.nbformat import v2
 from IPython.nbformat import v1
 
 from IPython.nbformat.v3 import (
     NotebookNode,
     new_code_cell, new_text_cell, new_notebook, new_output, new_worksheet,
     parse_filename, new_metadata, new_author, new_heading_cell, nbformat,
     nbformat_minor,
 )
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 current_nbformat = nbformat
 current_nbformat_minor = nbformat_minor
 
 
+class NBFormatError(ValueError):
+    pass
 
-class NBFormatError(Exception):
+class NotJSONError(ValueError):
     pass
 
 
 def parse_json(s, **kwargs):
     """Parse a string into a (nbformat, dict) tuple."""
-    d = json.loads(s, **kwargs)
+    try:
+        d = json.loads(s, **kwargs)
+    except ValueError:
+        raise NotJSONError("Notebook does not appear to be JSON: %r" % s[:16])
     nbf = d.get('nbformat', 1)
     nbm = d.get('nbformat_minor', 0)
     return nbf, nbm, d
 
 
 def parse_py(s, **kwargs):
     """Parse a string into a (nbformat, string) tuple."""
     nbf = current_nbformat
     nbm = current_nbformat_minor
     
     pattern = r'# <nbformat>(?P<nbformat>\d+[\.\d+]*)</nbformat>'
     m = re.search(pattern,s)
     if m is not None:
         digits = m.group('nbformat').split('.')
         nbf = int(digits[0])
         if len(digits) > 1:
             nbm = int(digits[1])
 
     return nbf, nbm, s
 
 
 def reads_json(s, **kwargs):
     """Read a JSON notebook from a string and return the NotebookNode object."""
     nbf, minor, d = parse_json(s, **kwargs)
     if nbf == 1:
         nb = v1.to_notebook_json(d, **kwargs)
         nb = v3.convert_to_this_nbformat(nb, orig_version=1)
     elif nbf == 2:
         nb = v2.to_notebook_json(d, **kwargs)
         nb = v3.convert_to_this_nbformat(nb, orig_version=2)
     elif nbf == 3:
         nb = v3.to_notebook_json(d, **kwargs)
         nb = v3.convert_to_this_nbformat(nb, orig_version=3, orig_minor=minor)
     else:
-        raise NBFormatError('Unsupported JSON nbformat version: %i' % nbf)
+        raise NBFormatError('Unsupported JSON nbformat version %s (supported version: %i)' % (nbf, 3))
     return nb
 
 
 def writes_json(nb, **kwargs):
     return v3.writes_json(nb, **kwargs)
 
 
 def reads_py(s, **kwargs):
     """Read a .py notebook from a string and return the NotebookNode object."""
     nbf, nbm, s = parse_py(s, **kwargs)
     if nbf == 2:
         nb = v2.to_notebook_py(s, **kwargs)
     elif nbf == 3:
         nb = v3.to_notebook_py(s, **kwargs)
     else:
         raise NBFormatError('Unsupported PY nbformat version: %i' % nbf)
     return nb
 
 
 def writes_py(nb, **kwargs):
     return v3.writes_py(nb, **kwargs)
 
 
 # High level API
 
 
 def reads(s, format, **kwargs):
     """Read a notebook from a string and return the NotebookNode object.
 
     This function properly handles notebooks of any version. The notebook
     returned will always be in the current version's format.
 
     Parameters
     ----------
     s : unicode
         The raw unicode string to read the notebook from.
     format : (u'json', u'ipynb', u'py')
         The format that the string is in.
 
     Returns
     -------
     nb : NotebookNode
         The notebook that was read.
     """
     format = unicode(format)
     if format == u'json' or format == u'ipynb':
         return reads_json(s, **kwargs)
     elif format == u'py':
         return reads_py(s, **kwargs)
     else:
         raise NBFormatError('Unsupported format: %s' % format)
 
 
 def writes(nb, format, **kwargs):
     """Write a notebook to a string in a given format in the current nbformat version.
 
     This function always writes the notebook in the current nbformat version.
 
     Parameters
     ----------
     nb : NotebookNode
         The notebook to write.
     format : (u'json', u'ipynb', u'py')
         The format to write the notebook in.
 
     Returns
     -------
     s : unicode
         The notebook string.
     """
     format = unicode(format)
     if format == u'json' or format == u'ipynb':
         return writes_json(nb, **kwargs)
     elif format == u'py':
         return writes_py(nb, **kwargs)
     else:
         raise NBFormatError('Unsupported format: %s' % format)
 
 
 def read(fp, format, **kwargs):
     """Read a notebook from a file and return the NotebookNode object.
 
     This function properly handles notebooks of any version. The notebook
     returned will always be in the current version's format.
 
     Parameters
     ----------
     fp : file
         Any file-like object with a read method.
     format : (u'json', u'ipynb', u'py')
         The format that the string is in.
 
     Returns
     -------
     nb : NotebookNode
         The notebook that was read.
     """
     return reads(fp.read(), format, **kwargs)
 
 
 def write(nb, fp, format, **kwargs):
     """Write a notebook to a file in a given format in the current nbformat version.
 
     This function always writes the notebook in the current nbformat version.
 
     Parameters
     ----------
     nb : NotebookNode
         The notebook to write.
     fp : file
         Any file-like object with a write method.
     format : (u'json', u'ipynb', u'py')
         The format to write the notebook in.
 
     Returns
     -------
     s : unicode
         The notebook string.
     """
     return fp.write(writes(nb, format, **kwargs))
 
 def _convert_to_metadata():
     """Convert to a notebook having notebook metadata."""
     import glob
     for fname in glob.glob('*.ipynb'):
         print('Converting file:',fname)
         with open(fname,'r') as f:
             nb = read(f,u'json')
         md = new_metadata()
         if u'name' in nb:
             md.name = nb.name
             del nb[u'name']            
         nb.metadata = md
         with open(fname,'w') as f:
             write(nb, f, u'json')