move _encode_binary to jsonutil.encode_images

And fix identification of PNG/JPEG data, which could be double-encoded when using a JSON library that decodes to str instead of unicode (simplejson 2.6, for instance).

Changes are tested.

IPython/utils/jsonutil.py

@@ -1,166 +1,185 b''
 """Utilities to manipulate JSON objects.
 """
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2010-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING.txt, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 # stdlib
 import re
 import sys
 import types
+from base64 import encodestring
 from datetime import datetime
 
 from IPython.utils import py3compat
 from IPython.utils.encoding import DEFAULT_ENCODING
 from IPython.utils import text
 next_attr_name = '__next__' if py3compat.PY3 else 'next'
 
 #-----------------------------------------------------------------------------
 # Globals and constants
 #-----------------------------------------------------------------------------
 
 # timestamp formats
 ISO8601="%Y-%m-%dT%H:%M:%S.%f"
 ISO8601_PAT=re.compile(r"^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d+$")
 
 #-----------------------------------------------------------------------------
 # Classes and functions
 #-----------------------------------------------------------------------------
 
 def rekey(dikt):
     """Rekey a dict that has been forced to use str keys where there should be
     ints by json."""
     for k in dikt.iterkeys():
         if isinstance(k, basestring):
             ik=fk=None
             try:
                 ik = int(k)
             except ValueError:
                 try:
                     fk = float(k)
                 except ValueError:
                     continue
             if ik is not None:
                 nk = ik
             else:
                 nk = fk
             if nk in dikt:
                 raise KeyError("already have key %r"%nk)
             dikt[nk] = dikt.pop(k)
     return dikt
 
 
 def extract_dates(obj):
     """extract ISO8601 dates from unpacked JSON"""
     if isinstance(obj, dict):
         obj = dict(obj) # don't clobber
         for k,v in obj.iteritems():
             obj[k] = extract_dates(v)
     elif isinstance(obj, (list, tuple)):
         obj = [ extract_dates(o) for o in obj ]
     elif isinstance(obj, basestring):
         if ISO8601_PAT.match(obj):
             obj = datetime.strptime(obj, ISO8601)
     return obj
 
 def squash_dates(obj):
     """squash datetime objects into ISO8601 strings"""
     if isinstance(obj, dict):
         obj = dict(obj) # don't clobber
         for k,v in obj.iteritems():
             obj[k] = squash_dates(v)
     elif isinstance(obj, (list, tuple)):
         obj = [ squash_dates(o) for o in obj ]
     elif isinstance(obj, datetime):
         obj = obj.strftime(ISO8601)
     return obj
     
 def date_default(obj):
     """default function for packing datetime objects in JSON."""
     if isinstance(obj, datetime):
         return obj.strftime(ISO8601)
     else:
         raise TypeError("%r is not JSON serializable"%obj)
 
 
+# constants for identifying png/jpeg data
+PNG = b'\x89PNG\r\n\x1a\n'
+JPEG = b'\xff\xd8'
+
+def encode_images(format_dict):
+    """b64-encodes images in a displaypub format dict
+    
+    Perhaps this should be handled in json_clean itself?
+    """
+    encoded = format_dict.copy()
+    pngdata = format_dict.get('image/png')
+    if isinstance(pngdata, bytes) and pngdata[:8] == PNG:
+        encoded['image/png'] = encodestring(pngdata).decode('ascii')
+    jpegdata = format_dict.get('image/jpeg')
+    if isinstance(jpegdata, bytes) and jpegdata[:2] == JPEG:
+        encoded['image/jpeg'] = encodestring(jpegdata).decode('ascii')
+    return encoded
+
 
 def json_clean(obj):
     """Clean an object to ensure it's safe to encode in JSON.
     
     Atomic, immutable objects are returned unmodified.  Sets and tuples are
     converted to lists, lists are copied and dicts are also copied.
 
     Note: dicts whose keys could cause collisions upon encoding (such as a dict
     with both the number 1 and the string '1' as keys) will cause a ValueError
     to be raised.
 
     Parameters
     ----------
     obj : any python object
 
     Returns
     -------
     out : object
     
       A version of the input which will not cause an encoding error when
       encoded as JSON.  Note that this function does not *encode* its inputs,
       it simply sanitizes it so that there will be no encoding errors later.
 
     Examples
     --------
     >>> json_clean(4)
     4
     >>> json_clean(range(10))
     [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
     >>> sorted(json_clean(dict(x=1, y=2)).items())
     [('x', 1), ('y', 2)]
     >>> sorted(json_clean(dict(x=1, y=2, z=[1,2,3])).items())
     [('x', 1), ('y', 2), ('z', [1, 2, 3])]
     >>> json_clean(True)
     True
     """
     # types that are 'atomic' and ok in json as-is.  bool doesn't need to be
     # listed explicitly because bools pass as int instances
     atomic_ok = (unicode, int, float, types.NoneType)
     
     # containers that we need to convert into lists
     container_to_list = (tuple, set, types.GeneratorType)
     
     if isinstance(obj, atomic_ok):
         return obj
     
     if isinstance(obj, bytes):
         return obj.decode(DEFAULT_ENCODING, 'replace')
     
     if isinstance(obj, container_to_list) or (
         hasattr(obj, '__iter__') and hasattr(obj, next_attr_name)):
         obj = list(obj)
         
     if isinstance(obj, list):
         return [json_clean(x) for x in obj]
 
     if isinstance(obj, dict):
         # First, validate that the dict won't lose data in conversion due to
         # key collisions after stringification.  This can happen with keys like
         # True and 'true' or 1 and '1', which collide in JSON.
         nkeys = len(obj)
         nkeys_collapsed = len(set(map(str, obj)))
         if nkeys != nkeys_collapsed:
             raise ValueError('dict can not be safely converted to JSON: '
                              'key collision would lead to dropped values')
         # If all OK, proceed by making the new dict that will be json-safe
         out = {}
         for k,v in obj.iteritems():
             out[str(k)] = json_clean(v)
         return out
 
     # If we get here, we don't know how to handle the object, so we just get
     # its repr and return that.  This will catch lambdas, open sockets, class
     # objects, and any other complicated contraption that json can't encode
     return repr(obj)

IPython/utils/tests/test_jsonutil.py

@@ -1,72 +1,104 b''
 """Test suite for our JSON utilities.
 """
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2010-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING.txt, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 # stdlib
 import json
+from base64 import decodestring
 
 # third party
 import nose.tools as nt
 
 # our own
-from ..jsonutil import json_clean
+from IPython.testing import decorators as dec
+from ..jsonutil import json_clean, encode_images
+from ..py3compat import unicode_to_str, str_to_bytes
 
 #-----------------------------------------------------------------------------
 # Test functions
 #-----------------------------------------------------------------------------
 
 def test():
     # list of input/expected output.  Use None for the expected output if it
     # can be the same as the input.
     pairs = [(1, None), # start with scalars
              (1.0, None),
              ('a', None),
              (True, None),
              (False, None),
              (None, None),
              # complex numbers for now just go to strings, as otherwise they
              # are unserializable
              (1j, '1j'),
              # Containers
              ([1, 2], None),
              ((1, 2), [1, 2]),
              (set([1, 2]), [1, 2]),
              (dict(x=1), None),
              ({'x': 1, 'y':[1,2,3], '1':'int'}, None),
              # More exotic objects
              ((x for x in range(3)), [0, 1, 2]),
              (iter([1, 2]), [1, 2]),
              ]
     
     for val, jval in pairs:
         if jval is None:
             jval = val
         out = json_clean(val)
         # validate our cleanup
         nt.assert_equal(out, jval)
         # and ensure that what we return, indeed encodes cleanly
         json.loads(json.dumps(out))
 
 
+
[e-mail]
+def test_encode_images():
+    # invalid data, but the header and footer are from real files
+    pngdata = b'\x89PNG\r\n\x1a\nblahblahnotactuallyvalidIEND\xaeB`\x82'
+    jpegdata = b'\xff\xd8\xff\xe0\x00\x10JFIFblahblahjpeg(\xa0\x0f\xff\xd9'
+    
+    fmt = {
+        'image/png'  : pngdata,
+        'image/jpeg' : jpegdata,
+    }
+    encoded = encode_images(fmt)
+    for key, value in fmt.iteritems():
+        # encoded has unicode, want bytes
+        decoded = decodestring(encoded[key].encode('ascii'))
+        yield nt.assert_equal(decoded, value)
+    encoded2 = encode_images(encoded)
+    yield nt.assert_equal(encoded, encoded2)
+    
+    b64_str = {}
+    for key, encoded in encoded.iteritems():
+        b64_str[key] = unicode_to_str(encoded)
+    encoded3 = encode_images(b64_str)
+    yield nt.assert_equal(encoded3, b64_str)
+    for key, value in fmt.iteritems():
+        # encoded3 has str, want bytes
+        decoded = decodestring(str_to_bytes(encoded3[key]))
+        yield nt.assert_equal(decoded, value)
+
 def test_lambda():
     jc = json_clean(lambda : 1)
     assert isinstance(jc, str)
     assert '<lambda>' in jc
     json.dumps(jc)
 
 
 def test_exception():
     bad_dicts = [{1:'number', '1':'string'},
                  {True:'bool', 'True':'string'},
                  ]
     for d in bad_dicts:
         nt.assert_raises(ValueError, json_clean, d)
     

IPython/zmq/displayhook.py

@@ -1,75 +1,63 b''
 import __builtin__
 import sys
-from base64 import encodestring
 
 from IPython.core.displayhook import DisplayHook
+from IPython.utils.jsonutil import encode_images
 from IPython.utils.traitlets import Instance, Dict
 from session import extract_header, Session
 
 class ZMQDisplayHook(object):
     """A simple displayhook that publishes the object's repr over a ZeroMQ
     socket."""
     topic=None
 
     def __init__(self, session, pub_socket):
         self.session = session
         self.pub_socket = pub_socket
         self.parent_header = {}
 
     def __call__(self, obj):
         if obj is None:
             return
 
         __builtin__._ = obj
         sys.stdout.flush()
         sys.stderr.flush()
         msg = self.session.send(self.pub_socket, u'pyout', {u'data':repr(obj)},
                                parent=self.parent_header, ident=self.topic)
 
     def set_parent(self, parent):
         self.parent_header = extract_header(parent)
 
 
-def _encode_binary(format_dict):
-    encoded = format_dict.copy()
-    pngdata = format_dict.get('image/png')
-    if isinstance(pngdata, bytes):
-        encoded['image/png'] = encodestring(pngdata).decode('ascii')
-    jpegdata = format_dict.get('image/jpeg')
-    if isinstance(jpegdata, bytes):
-        encoded['image/jpeg'] = encodestring(jpegdata).decode('ascii')
-    
-    return encoded
-
-
 class ZMQShellDisplayHook(DisplayHook):
     """A displayhook subclass that publishes data using ZeroMQ. This is intended
     to work with an InteractiveShell instance. It sends a dict of different
     representations of the object."""
     topic=None
 
     session = Instance(Session)
     pub_socket = Instance('zmq.Socket')
     parent_header = Dict({})
 
     def set_parent(self, parent):
         """Set the parent for outbound messages."""
         self.parent_header = extract_header(parent)
 
     def start_displayhook(self):
         self.msg = self.session.msg(u'pyout', {}, parent=self.parent_header)
 
     def write_output_prompt(self):
         """Write the output prompt."""
         self.msg['content']['execution_count'] = self.prompt_count
 
     def write_format_data(self, format_dict):
-        self.msg['content']['data'] = _encode_binary(format_dict)
+        self.msg['content']['data'] = encode_images(format_dict)
 
     def finish_displayhook(self):
         """Finish up all displayhook activities."""
         sys.stdout.flush()
         sys.stderr.flush()
         self.session.send(self.pub_socket, self.msg, ident=self.topic)
         self.msg = None
 

IPython/zmq/zmqshell.py

@@ -1,581 +1,581 b''
 """A ZMQ-based subclass of InteractiveShell.
 
 This code is meant to ease the refactoring of the base InteractiveShell into
 something with a cleaner architecture for 2-process use, without actually
 breaking InteractiveShell itself.  So we're doing something a bit ugly, where
 we subclass and override what we want to fix.  Once this is working well, we
 can go back to the base class and refactor the code for a cleaner inheritance
 implementation that doesn't rely on so much monkeypatching.
 
 But this lets us maintain a fully working IPython as we develop the new
 machinery.  This should thus be thought of as scaffolding.
 """
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 from __future__ import print_function
 
 # Stdlib
 import os
 import sys
 import time
 
 # System library imports
 from zmq.eventloop import ioloop
 
 # Our own
 from IPython.core.interactiveshell import (
     InteractiveShell, InteractiveShellABC
 )
 from IPython.core import page
 from IPython.core.autocall import ZMQExitAutocall
 from IPython.core.displaypub import DisplayPublisher
 from IPython.core.magics import MacroToEdit, CodeMagics
 from IPython.core.magic import magics_class, line_magic, Magics
 from IPython.core.payloadpage import install_payload_page
 from IPython.lib.kernel import (
     get_connection_file, get_connection_info, connect_qtconsole
 )
 from IPython.testing.skipdoctest import skip_doctest
 from IPython.utils import io
-from IPython.utils.jsonutil import json_clean
+from IPython.utils.jsonutil import json_clean, encode_images
 from IPython.utils.process import arg_split
 from IPython.utils import py3compat
 from IPython.utils.traitlets import Instance, Type, Dict, CBool, CBytes
 from IPython.utils.warn import warn, error
-from IPython.zmq.displayhook import ZMQShellDisplayHook, _encode_binary
+from IPython.zmq.displayhook import ZMQShellDisplayHook
 from IPython.zmq.session import extract_header
 from session import Session
 
 #-----------------------------------------------------------------------------
 # Functions and classes
 #-----------------------------------------------------------------------------
 
 class ZMQDisplayPublisher(DisplayPublisher):
     """A display publisher that publishes data using a ZeroMQ PUB socket."""
 
     session = Instance(Session)
     pub_socket = Instance('zmq.Socket')
     parent_header = Dict({})
     topic = CBytes(b'displaypub')
 
     def set_parent(self, parent):
         """Set the parent for outbound messages."""
         self.parent_header = extract_header(parent)
     
     def _flush_streams(self):
         """flush IO Streams prior to display"""
         sys.stdout.flush()
         sys.stderr.flush()
 
     def publish(self, source, data, metadata=None):
         self._flush_streams()
         if metadata is None:
             metadata = {}
         self._validate_data(source, data, metadata)
         content = {}
         content['source'] = source
-        content['data'] = _encode_binary(data)
+        content['data'] = encode_images(data)
         content['metadata'] = metadata
         self.session.send(
             self.pub_socket, u'display_data', json_clean(content),
             parent=self.parent_header, ident=self.topic,
         )
 
     def clear_output(self, stdout=True, stderr=True, other=True):
         content = dict(stdout=stdout, stderr=stderr, other=other)
         
         if stdout:
             print('\r', file=sys.stdout, end='')
         if stderr:
             print('\r', file=sys.stderr, end='')
         
         self._flush_streams()
         
         self.session.send(
             self.pub_socket, u'clear_output', content,
             parent=self.parent_header, ident=self.topic,
         )
 
 @magics_class
 class KernelMagics(Magics):
     #------------------------------------------------------------------------
     # Magic overrides
     #------------------------------------------------------------------------
     # Once the base class stops inheriting from magic, this code needs to be
     # moved into a separate machinery as well.  For now, at least isolate here
     # the magics which this class needs to implement differently from the base
     # class, or that are unique to it.
 
     @line_magic
     def doctest_mode(self, parameter_s=''):
         """Toggle doctest mode on and off.
 
         This mode is intended to make IPython behave as much as possible like a
         plain Python shell, from the perspective of how its prompts, exceptions
         and output look.  This makes it easy to copy and paste parts of a
         session into doctests.  It does so by:
 
         - Changing the prompts to the classic ``>>>`` ones.
         - Changing the exception reporting mode to 'Plain'.
         - Disabling pretty-printing of output.
 
         Note that IPython also supports the pasting of code snippets that have
         leading '>>>' and '...' prompts in them.  This means that you can paste
         doctests from files or docstrings (even if they have leading
         whitespace), and the code will execute correctly.  You can then use
         '%history -t' to see the translated history; this will give you the
         input after removal of all the leading prompts and whitespace, which
         can be pasted back into an editor.
 
         With these features, you can switch into this mode easily whenever you
         need to do testing and changes to doctests, without having to leave
         your existing IPython session.
         """
 
         from IPython.utils.ipstruct import Struct
 
         # Shorthands
         shell = self.shell
         disp_formatter = self.shell.display_formatter
         ptformatter = disp_formatter.formatters['text/plain']
         # dstore is a data store kept in the instance metadata bag to track any
         # changes we make, so we can undo them later.
         dstore = shell.meta.setdefault('doctest_mode', Struct())
         save_dstore = dstore.setdefault
 
         # save a few values we'll need to recover later
         mode = save_dstore('mode', False)
         save_dstore('rc_pprint', ptformatter.pprint)
         save_dstore('rc_plain_text_only',disp_formatter.plain_text_only)
         save_dstore('xmode', shell.InteractiveTB.mode)
 
         if mode == False:
             # turn on
             ptformatter.pprint = False
             disp_formatter.plain_text_only = True
             shell.magic('xmode Plain')
         else:
             # turn off
             ptformatter.pprint = dstore.rc_pprint
             disp_formatter.plain_text_only = dstore.rc_plain_text_only
             shell.magic("xmode " + dstore.xmode)
 
         # Store new mode and inform on console
         dstore.mode = bool(1-int(mode))
         mode_label = ['OFF','ON'][dstore.mode]
         print('Doctest mode is:', mode_label)
 
         # Send the payload back so that clients can modify their prompt display
         payload = dict(
             source='IPython.zmq.zmqshell.ZMQInteractiveShell.doctest_mode',
             mode=dstore.mode)
         shell.payload_manager.write_payload(payload)
         
     
     _find_edit_target = CodeMagics._find_edit_target
 
     @skip_doctest
     @line_magic
     def edit(self, parameter_s='', last_call=['','']):
         """Bring up an editor and execute the resulting code.
 
         Usage:
           %edit [options] [args]
 
         %edit runs an external text editor. You will need to set the command for
         this editor via the ``TerminalInteractiveShell.editor`` option in your
         configuration file before it will work.
 
         This command allows you to conveniently edit multi-line code right in
         your IPython session.
 
         If called without arguments, %edit opens up an empty editor with a
         temporary file and will execute the contents of this file when you
         close it (don't forget to save it!).
 
 
         Options:
 
         -n <number>: open the editor at a specified line number.  By default,
         the IPython editor hook uses the unix syntax 'editor +N filename', but
         you can configure this by providing your own modified hook if your
         favorite editor supports line-number specifications with a different
         syntax.
 
         -p: this will call the editor with the same data as the previous time
         it was used, regardless of how long ago (in your current session) it
         was.
 
         -r: use 'raw' input.  This option only applies to input taken from the
         user's history.  By default, the 'processed' history is used, so that
         magics are loaded in their transformed version to valid Python.  If
         this option is given, the raw input as typed as the command line is
         used instead.  When you exit the editor, it will be executed by
         IPython's own processor.
 
         -x: do not execute the edited code immediately upon exit. This is
         mainly useful if you are editing programs which need to be called with
         command line arguments, which you can then do using %run.
 
 
         Arguments:
 
         If arguments are given, the following possibilites exist:
 
         - The arguments are numbers or pairs of colon-separated numbers (like
         1 4:8 9). These are interpreted as lines of previous input to be
         loaded into the editor. The syntax is the same of the %macro command.
 
         - If the argument doesn't start with a number, it is evaluated as a
         variable and its contents loaded into the editor. You can thus edit
         any string which contains python code (including the result of
         previous edits).
 
         - If the argument is the name of an object (other than a string),
         IPython will try to locate the file where it was defined and open the
         editor at the point where it is defined. You can use `%edit function`
         to load an editor exactly at the point where 'function' is defined,
         edit it and have the file be executed automatically.
 
         If the object is a macro (see %macro for details), this opens up your
         specified editor with a temporary file containing the macro's data.
         Upon exit, the macro is reloaded with the contents of the file.
 
         Note: opening at an exact line is only supported under Unix, and some
         editors (like kedit and gedit up to Gnome 2.8) do not understand the
         '+NUMBER' parameter necessary for this feature. Good editors like
         (X)Emacs, vi, jed, pico and joe all do.
 
         - If the argument is not found as a variable, IPython will look for a
         file with that name (adding .py if necessary) and load it into the
         editor. It will execute its contents with execfile() when you exit,
         loading any code in the file into your interactive namespace.
 
         After executing your code, %edit will return as output the code you
         typed in the editor (except when it was an existing file). This way
         you can reload the code in further invocations of %edit as a variable,
         via _<NUMBER> or Out[<NUMBER>], where <NUMBER> is the prompt number of
         the output.
 
         Note that %edit is also available through the alias %ed.
 
         This is an example of creating a simple function inside the editor and
         then modifying it. First, start up the editor:
 
         In [1]: ed
         Editing... done. Executing edited code...
         Out[1]: 'def foo():n    print "foo() was defined in an editing session"n'
 
         We can then call the function foo():
 
         In [2]: foo()
         foo() was defined in an editing session
 
         Now we edit foo.  IPython automatically loads the editor with the
         (temporary) file where foo() was previously defined:
 
         In [3]: ed foo
         Editing... done. Executing edited code...
 
         And if we call foo() again we get the modified version:
 
         In [4]: foo()
         foo() has now been changed!
 
         Here is an example of how to edit a code snippet successive
         times. First we call the editor:
 
         In [5]: ed
         Editing... done. Executing edited code...
         hello
         Out[5]: "print 'hello'n"
 
         Now we call it again with the previous output (stored in _):
 
         In [6]: ed _
         Editing... done. Executing edited code...
         hello world
         Out[6]: "print 'hello world'n"
 
         Now we call it with the output #8 (stored in _8, also as Out[8]):
 
         In [7]: ed _8
         Editing... done. Executing edited code...
         hello again
         Out[7]: "print 'hello again'n"
         """
 
         opts,args = self.parse_options(parameter_s,'prn:')
 
         try:
             filename, lineno, _ = CodeMagics._find_edit_target(self.shell, args, opts, last_call)
         except MacroToEdit as e:
             # TODO: Implement macro editing over 2 processes.
             print("Macro editing not yet implemented in 2-process model.")
             return
 
         # Make sure we send to the client an absolute path, in case the working
         # directory of client and kernel don't match
         filename = os.path.abspath(filename)
 
         payload = {
             'source' : 'IPython.zmq.zmqshell.ZMQInteractiveShell.edit_magic',
             'filename' : filename,
             'line_number' : lineno
         }
         self.shell.payload_manager.write_payload(payload)
 
     # A few magics that are adapted to the specifics of using pexpect and a
     # remote terminal
 
     @line_magic
     def clear(self, arg_s):
         """Clear the terminal."""
         if os.name == 'posix':
             self.shell.system("clear")
         else:
             self.shell.system("cls")
 
     if os.name == 'nt':
         # This is the usual name in windows
         cls = line_magic('cls')(clear)
 
     # Terminal pagers won't work over pexpect, but we do have our own pager
 
     @line_magic
     def less(self, arg_s):
         """Show a file through the pager.
 
         Files ending in .py are syntax-highlighted."""
         cont = open(arg_s).read()
         if arg_s.endswith('.py'):
             cont = self.shell.pycolorize(cont)
         page.page(cont)
 
     more = line_magic('more')(less)
 
     # Man calls a pager, so we also need to redefine it
     if os.name == 'posix':
         @line_magic
         def man(self, arg_s):
             """Find the man page for the given command and display in pager."""
             page.page(self.shell.getoutput('man %s | col -b' % arg_s,
                                            split=False))
 
     @line_magic
     def connect_info(self, arg_s):
         """Print information for connecting other clients to this kernel
         
         It will print the contents of this session's connection file, as well as
         shortcuts for local clients.
         
         In the simplest case, when called from the most recently launched kernel,
         secondary clients can be connected, simply with:
         
         $> ipython <app> --existing
         
         """
         
         from IPython.core.application import BaseIPythonApplication as BaseIPApp
         
         if BaseIPApp.initialized():
             app = BaseIPApp.instance()
             security_dir = app.profile_dir.security_dir
             profile = app.profile
         else:
             profile = 'default'
             security_dir = ''
         
         try:
             connection_file = get_connection_file()
             info = get_connection_info(unpack=False)
         except Exception as e:
             error("Could not get connection info: %r" % e)
             return
         
         # add profile flag for non-default profile
         profile_flag = "--profile %s" % profile if profile != 'default' else ""
         
         # if it's in the security dir, truncate to basename
         if security_dir == os.path.dirname(connection_file):
             connection_file = os.path.basename(connection_file)
         
         
         print (info + '\n')
         print ("Paste the above JSON into a file, and connect with:\n"
             "    $> ipython <app> --existing <file>\n"
             "or, if you are local, you can connect with just:\n"
             "    $> ipython <app> --existing {0} {1}\n"
             "or even just:\n"
             "    $> ipython <app> --existing {1}\n"
             "if this is the most recent IPython session you have started.".format(
             connection_file, profile_flag
             )
         )
 
     @line_magic
     def qtconsole(self, arg_s):
         """Open a qtconsole connected to this kernel.
         
         Useful for connecting a qtconsole to running notebooks, for better
         debugging.
         """
         
         # %qtconsole should imply bind_kernel for engines:
         try:
             from IPython.parallel import bind_kernel
         except ImportError:
             # technically possible, because parallel has higher pyzmq min-version
             pass
         else:
             bind_kernel()
         
         try:
             p = connect_qtconsole(argv=arg_split(arg_s, os.name=='posix'))
         except Exception as e:
             error("Could not start qtconsole: %r" % e)
             return
 
 def safe_unicode(e):
     """unicode(e) with various fallbacks. Used for exceptions, which may not be
     safe to call unicode() on.
     """
     try:
         return unicode(e)
     except UnicodeError:
         pass
 
     try:
         return py3compat.str_to_unicode(str(e))
     except UnicodeError:
         pass
 
     try:
         return py3compat.str_to_unicode(repr(e))
     except UnicodeError:
         pass
 
     return u'Unrecoverably corrupt evalue'
 
 
 class ZMQInteractiveShell(InteractiveShell):
     """A subclass of InteractiveShell for ZMQ."""
 
     displayhook_class = Type(ZMQShellDisplayHook)
     display_pub_class = Type(ZMQDisplayPublisher)
 
     # Override the traitlet in the parent class, because there's no point using
     # readline for the kernel. Can be removed when the readline code is moved
     # to the terminal frontend.
     colors_force = CBool(True)
     readline_use = CBool(False)
     # autoindent has no meaning in a zmqshell, and attempting to enable it
     # will print a warning in the absence of readline.
     autoindent = CBool(False)
 
     exiter = Instance(ZMQExitAutocall)
     def _exiter_default(self):
         return ZMQExitAutocall(self)
     
     def _exit_now_changed(self, name, old, new):
         """stop eventloop when exit_now fires"""
         if new:
             loop = ioloop.IOLoop.instance()
             loop.add_timeout(time.time()+0.1, loop.stop)
 
     keepkernel_on_exit = None
 
     # Over ZeroMQ, GUI control isn't done with PyOS_InputHook as there is no
     # interactive input being read; we provide event loop support in ipkernel
     from .eventloops import enable_gui
     enable_gui = staticmethod(enable_gui)
 
     def init_environment(self):
         """Configure the user's environment.
 
         """
         env = os.environ
         # These two ensure 'ls' produces nice coloring on BSD-derived systems
         env['TERM'] = 'xterm-color'
         env['CLICOLOR'] = '1'
         # Since normal pagers don't work at all (over pexpect we don't have
         # single-key control of the subprocess), try to disable paging in
         # subprocesses as much as possible.
         env['PAGER'] = 'cat'
         env['GIT_PAGER'] = 'cat'
         
         # And install the payload version of page.
         install_payload_page()
 
     def auto_rewrite_input(self, cmd):
         """Called to show the auto-rewritten input for autocall and friends.
 
         FIXME: this payload is currently not correctly processed by the
         frontend.
         """
         new = self.prompt_manager.render('rewrite') + cmd
         payload = dict(
             source='IPython.zmq.zmqshell.ZMQInteractiveShell.auto_rewrite_input',
             transformed_input=new,
             )
         self.payload_manager.write_payload(payload)
 
     def ask_exit(self):
         """Engage the exit actions."""
         self.exit_now = True
         payload = dict(
             source='IPython.zmq.zmqshell.ZMQInteractiveShell.ask_exit',
             exit=True,
             keepkernel=self.keepkernel_on_exit,
             )
         self.payload_manager.write_payload(payload)
 
     def _showtraceback(self, etype, evalue, stb):
 
         exc_content = {
             u'traceback' : stb,
             u'ename' : unicode(etype.__name__),
             u'evalue' : safe_unicode(evalue)
         }
 
         dh = self.displayhook
         # Send exception info over pub socket for other clients than the caller
         # to pick up
         topic = None
         if dh.topic:
             topic = dh.topic.replace(b'pyout', b'pyerr')
         
         exc_msg = dh.session.send(dh.pub_socket, u'pyerr', json_clean(exc_content), dh.parent_header, ident=topic)
 
         # FIXME - Hack: store exception info in shell object.  Right now, the
         # caller is reading this info after the fact, we need to fix this logic
         # to remove this hack.  Even uglier, we need to store the error status
         # here, because in the main loop, the logic that sets it is being
         # skipped because runlines swallows the exceptions.
         exc_content[u'status'] = u'error'
         self._reply_content = exc_content
         # /FIXME
 
         return exc_content
 
     def set_next_input(self, text):
         """Send the specified text to the frontend to be presented at the next
         input cell."""
         payload = dict(
             source='IPython.zmq.zmqshell.ZMQInteractiveShell.set_next_input',
             text=text
         )
         self.payload_manager.write_payload(payload)
     
     #-------------------------------------------------------------------------
     # Things related to magics
     #-------------------------------------------------------------------------
 
     def init_magics(self):
         super(ZMQInteractiveShell, self).init_magics()
         self.register_magics(KernelMagics)
 
 
 
 InteractiveShellABC.register(ZMQInteractiveShell)