Avoid loading readline in the kernel

This bit of code was loading readline even when there was no need for
it. In a Qt console or notebook, try:

    'readline' in sys.modules
    'gnureadline' in sys.modules

I plan to rework this code more extensively once we've switched to
prompt_toolkit, but for now, this little fix should make the kernel
start slightly faster.

IPython/core/magics/basic.py

@@ -1,610 +1,612 b''
 """Implementation of basic magic functions."""
 
 from __future__ import print_function
 
 import io
 import sys
 from pprint import pformat
 
 from IPython.core import magic_arguments, page
 from IPython.core.error import UsageError
 from IPython.core.magic import Magics, magics_class, line_magic, magic_escapes
 from IPython.utils.text import format_screen, dedent, indent
 from IPython.testing.skipdoctest import skip_doctest
 from IPython.utils.ipstruct import Struct
 from IPython.utils.path import unquote_filename
 from IPython.utils.py3compat import unicode_type
 from IPython.utils.warn import warn, error
 
 
 class MagicsDisplay(object):
     def __init__(self, magics_manager):
         self.magics_manager = magics_manager
     
     def _lsmagic(self):
         """The main implementation of the %lsmagic"""
         mesc = magic_escapes['line']
         cesc = magic_escapes['cell']
         mman = self.magics_manager
         magics = mman.lsmagic()
         out = ['Available line magics:',
                mesc + ('  '+mesc).join(sorted(magics['line'])),
                '',
                'Available cell magics:',
                cesc + ('  '+cesc).join(sorted(magics['cell'])),
                '',
                mman.auto_status()]
         return '\n'.join(out)
 
     def _repr_pretty_(self, p, cycle):
         p.text(self._lsmagic())
     
     def __str__(self):
         return self._lsmagic()
     
     def _jsonable(self):
         """turn magics dict into jsonable dict of the same structure
         
         replaces object instances with their class names as strings
         """
         magic_dict = {}
         mman = self.magics_manager
         magics = mman.lsmagic()
         for key, subdict in magics.items():
             d = {}
             magic_dict[key] = d
             for name, obj in subdict.items():
                 try:
                     classname = obj.__self__.__class__.__name__
                 except AttributeError:
                     classname = 'Other'
                 
                 d[name] = classname
         return magic_dict
         
     def _repr_json_(self):
         return self._jsonable()
 
 
 @magics_class
 class BasicMagics(Magics):
     """Magics that provide central IPython functionality.
 
     These are various magics that don't fit into specific categories but that
     are all part of the base 'IPython experience'."""
 
     @magic_arguments.magic_arguments()
     @magic_arguments.argument(
         '-l', '--line', action='store_true',
         help="""Create a line magic alias."""
     )
     @magic_arguments.argument(
         '-c', '--cell', action='store_true',
         help="""Create a cell magic alias."""
     )
     @magic_arguments.argument(
         'name',
         help="""Name of the magic to be created."""
     )
     @magic_arguments.argument(
         'target',
         help="""Name of the existing line or cell magic."""
     )
     @line_magic
     def alias_magic(self, line=''):
         """Create an alias for an existing line or cell magic.
 
         Examples
         --------
         ::
 
           In [1]: %alias_magic t timeit
           Created `%t` as an alias for `%timeit`.
           Created `%%t` as an alias for `%%timeit`.
 
           In [2]: %t -n1 pass
           1 loops, best of 3: 954 ns per loop
 
           In [3]: %%t -n1
              ...: pass
              ...:
           1 loops, best of 3: 954 ns per loop
 
           In [4]: %alias_magic --cell whereami pwd
           UsageError: Cell magic function `%%pwd` not found.
           In [5]: %alias_magic --line whereami pwd
           Created `%whereami` as an alias for `%pwd`.
 
           In [6]: %whereami
           Out[6]: u'/home/testuser'
         """
         args = magic_arguments.parse_argstring(self.alias_magic, line)
         shell = self.shell
         mman = self.shell.magics_manager
         escs = ''.join(magic_escapes.values())
 
         target = args.target.lstrip(escs)
         name = args.name.lstrip(escs)
 
         # Find the requested magics.
         m_line = shell.find_magic(target, 'line')
         m_cell = shell.find_magic(target, 'cell')
         if args.line and m_line is None:
             raise UsageError('Line magic function `%s%s` not found.' %
                              (magic_escapes['line'], target))
         if args.cell and m_cell is None:
             raise UsageError('Cell magic function `%s%s` not found.' %
                              (magic_escapes['cell'], target))
 
         # If --line and --cell are not specified, default to the ones
         # that are available.
         if not args.line and not args.cell:
             if not m_line and not m_cell:
                 raise UsageError(
                     'No line or cell magic with name `%s` found.' % target
                 )
             args.line = bool(m_line)
             args.cell = bool(m_cell)
 
         if args.line:
             mman.register_alias(name, target, 'line')
             print('Created `%s%s` as an alias for `%s%s`.' % (
                 magic_escapes['line'], name,
                 magic_escapes['line'], target))
 
         if args.cell:
             mman.register_alias(name, target, 'cell')
             print('Created `%s%s` as an alias for `%s%s`.' % (
                 magic_escapes['cell'], name,
                 magic_escapes['cell'], target))
 
     @line_magic
     def lsmagic(self, parameter_s=''):
         """List currently available magic functions."""
         return MagicsDisplay(self.shell.magics_manager)
 
     def _magic_docs(self, brief=False, rest=False):
         """Return docstrings from magic functions."""
         mman = self.shell.magics_manager
         docs = mman.lsmagic_docs(brief, missing='No documentation')
 
         if rest:
             format_string = '**%s%s**::\n\n%s\n\n'
         else:
             format_string = '%s%s:\n%s\n'
 
         return ''.join(
             [format_string % (magic_escapes['line'], fname,
                               indent(dedent(fndoc)))
              for fname, fndoc in sorted(docs['line'].items())]
             +
             [format_string % (magic_escapes['cell'], fname,
                               indent(dedent(fndoc)))
              for fname, fndoc in sorted(docs['cell'].items())]
         )
 
     @line_magic
     def magic(self, parameter_s=''):
         """Print information about the magic function system.
 
         Supported formats: -latex, -brief, -rest
         """
 
         mode = ''
         try:
             mode = parameter_s.split()[0][1:]
         except IndexError:
             pass
 
         brief = (mode == 'brief')
         rest = (mode == 'rest')
         magic_docs = self._magic_docs(brief, rest)
 
         if mode == 'latex':
             print(self.format_latex(magic_docs))
             return
         else:
             magic_docs = format_screen(magic_docs)
 
         out = ["""
 IPython's 'magic' functions
 ===========================
 
 The magic function system provides a series of functions which allow you to
 control the behavior of IPython itself, plus a lot of system-type
 features. There are two kinds of magics, line-oriented and cell-oriented.
 
 Line magics are prefixed with the % character and work much like OS
 command-line calls: they get as an argument the rest of the line, where
 arguments are passed without parentheses or quotes.  For example, this will
 time the given statement::
 
         %timeit range(1000)
 
 Cell magics are prefixed with a double %%, and they are functions that get as
 an argument not only the rest of the line, but also the lines below it in a
 separate argument.  These magics are called with two arguments: the rest of the
 call line and the body of the cell, consisting of the lines below the first.
 For example::
 
         %%timeit x = numpy.random.randn((100, 100))
         numpy.linalg.svd(x)
 
 will time the execution of the numpy svd routine, running the assignment of x
 as part of the setup phase, which is not timed.
 
 In a line-oriented client (the terminal or Qt console IPython), starting a new
 input with %% will automatically enter cell mode, and IPython will continue
 reading input until a blank line is given.  In the notebook, simply type the
 whole cell as one entity, but keep in mind that the %% escape can only be at
 the very start of the cell.
 
 NOTE: If you have 'automagic' enabled (via the command line option or with the
 %automagic function), you don't need to type in the % explicitly for line
 magics; cell magics always require an explicit '%%' escape.  By default,
 IPython ships with automagic on, so you should only rarely need the % escape.
 
 Example: typing '%cd mydir' (without the quotes) changes your working directory
 to 'mydir', if it exists.
 
 For a list of the available magic functions, use %lsmagic. For a description
 of any of them, type %magic_name?, e.g. '%cd?'.
 
 Currently the magic system has the following functions:""",
        magic_docs,
        "Summary of magic functions (from %slsmagic):" % magic_escapes['line'],
        str(self.lsmagic()),
        ]
         page.page('\n'.join(out))
 
 
     @line_magic
     def page(self, parameter_s=''):
         """Pretty print the object and display it through a pager.
 
         %page [options] OBJECT
 
         If no object is given, use _ (last output).
 
         Options:
 
           -r: page str(object), don't pretty-print it."""
 
         # After a function contributed by Olivier Aubert, slightly modified.
 
         # Process options/args
         opts, args = self.parse_options(parameter_s, 'r')
         raw = 'r' in opts
 
         oname = args and args or '_'
         info = self.shell._ofind(oname)
         if info['found']:
             txt = (raw and str or pformat)( info['obj'] )
             page.page(txt)
         else:
             print('Object `%s` not found' % oname)
 
     @line_magic
     def profile(self, parameter_s=''):
         """Print your currently active IPython profile.
 
         See Also
         --------
         prun : run code using the Python profiler
                (:meth:`~IPython.core.magics.execution.ExecutionMagics.prun`)
         """
         warn("%profile is now deprecated. Please use get_ipython().profile instead.")
         from IPython.core.application import BaseIPythonApplication
         if BaseIPythonApplication.initialized():
             print(BaseIPythonApplication.instance().profile)
         else:
             error("profile is an application-level value, but you don't appear to be in an IPython application")
 
     @line_magic
     def pprint(self, parameter_s=''):
         """Toggle pretty printing on/off."""
         ptformatter = self.shell.display_formatter.formatters['text/plain']
         ptformatter.pprint = bool(1 - ptformatter.pprint)
         print('Pretty printing has been turned',
               ['OFF','ON'][ptformatter.pprint])
 
     @line_magic
     def colors(self, parameter_s=''):
         """Switch color scheme for prompts, info system and exception handlers.
 
         Currently implemented schemes: NoColor, Linux, LightBG.
 
         Color scheme names are not case-sensitive.
 
         Examples
         --------
         To get a plain black and white terminal::
 
           %colors nocolor
         """
         def color_switch_err(name):
             warn('Error changing %s color schemes.\n%s' %
                  (name, sys.exc_info()[1]))
 
 
         new_scheme = parameter_s.strip()
         if not new_scheme:
             raise UsageError(
                 "%colors: you must specify a color scheme. See '%colors?'")
         # local shortcut
         shell = self.shell
 
-        import IPython.utils.rlineimpl as readline
 
-        if not shell.colors_force and \
-                not readline.have_readline and \
-                (sys.platform == "win32" or sys.platform == "cli"):
-            msg = """\
+
+        if not shell.colors_force:
+            if sys.platform in {'win32', 'cli'}:
+                import IPython.utils.rlineimpl as readline
+                if not readline.have_readline:
+                    msg = """\
 Proper color support under MS Windows requires the pyreadline library.
 You can find it at:
 http://ipython.org/pyreadline.html
 
 Defaulting color scheme to 'NoColor'"""
-            new_scheme = 'NoColor'
-            warn(msg)
+                    new_scheme = 'NoColor'
+                    warn(msg)
 
-        # readline option is 0
-        if not shell.colors_force and not shell.has_readline:
-            new_scheme = 'NoColor'
+            elif not shell.has_readline:
+                # Coloured prompts get messed up without readline
+                # Will remove this check after switching to prompt_toolkit
+                new_scheme = 'NoColor'
 
         # Set prompt colors
         try:
             shell.prompt_manager.color_scheme = new_scheme
         except:
             color_switch_err('prompt')
         else:
             shell.colors = \
                    shell.prompt_manager.color_scheme_table.active_scheme_name
         # Set exception colors
         try:
             shell.InteractiveTB.set_colors(scheme = new_scheme)
             shell.SyntaxTB.set_colors(scheme = new_scheme)
         except:
             color_switch_err('exception')
 
         # Set info (for 'object?') colors
         if shell.color_info:
             try:
                 shell.inspector.set_active_scheme(new_scheme)
             except:
                 color_switch_err('object inspector')
         else:
             shell.inspector.set_active_scheme('NoColor')
 
     @line_magic
     def xmode(self, parameter_s=''):
         """Switch modes for the exception handlers.
 
         Valid modes: Plain, Context and Verbose.
 
         If called without arguments, acts as a toggle."""
 
         def xmode_switch_err(name):
             warn('Error changing %s exception modes.\n%s' %
                  (name,sys.exc_info()[1]))
 
         shell = self.shell
         new_mode = parameter_s.strip().capitalize()
         try:
             shell.InteractiveTB.set_mode(mode=new_mode)
             print('Exception reporting mode:',shell.InteractiveTB.mode)
         except:
             xmode_switch_err('user')
 
     @line_magic
     def quickref(self,arg):
         """ Show a quick reference sheet """
         from IPython.core.usage import quick_reference
         qr = quick_reference + self._magic_docs(brief=True)
         page.page(qr)
 
     @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.
         """
 
         # Shorthands
         shell = self.shell
         pm = shell.prompt_manager
         meta = shell.meta
         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 = 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('xmode',shell.InteractiveTB.mode)
         save_dstore('rc_separate_out',shell.separate_out)
         save_dstore('rc_separate_out2',shell.separate_out2)
         save_dstore('rc_prompts_pad_left',pm.justify)
         save_dstore('rc_separate_in',shell.separate_in)
         save_dstore('rc_active_types',disp_formatter.active_types)
         save_dstore('prompt_templates',(pm.in_template, pm.in2_template, pm.out_template))
 
         if not mode:
             # turn on
             pm.in_template = '>>> '
             pm.in2_template = '... '
             pm.out_template = ''
 
             # Prompt separators like plain python
             shell.separate_in = ''
             shell.separate_out = ''
             shell.separate_out2 = ''
 
             pm.justify = False
 
             ptformatter.pprint = False
             disp_formatter.active_types = ['text/plain']
 
             shell.magic('xmode Plain')
         else:
             # turn off
             pm.in_template, pm.in2_template, pm.out_template = dstore.prompt_templates
 
             shell.separate_in = dstore.rc_separate_in
 
             shell.separate_out = dstore.rc_separate_out
             shell.separate_out2 = dstore.rc_separate_out2
 
             pm.justify = dstore.rc_prompts_pad_left
 
             ptformatter.pprint = dstore.rc_pprint
             disp_formatter.active_types = dstore.rc_active_types
 
             shell.magic('xmode ' + dstore.xmode)
 
         # Store new mode and inform
         dstore.mode = bool(1-int(mode))
         mode_label = ['OFF','ON'][dstore.mode]
         print('Doctest mode is:', mode_label)
 
     @line_magic
     def gui(self, parameter_s=''):
         """Enable or disable IPython GUI event loop integration.
 
         %gui [GUINAME]
 
         This magic replaces IPython's threaded shells that were activated
         using the (pylab/wthread/etc.) command line flags.  GUI toolkits
         can now be enabled at runtime and keyboard
         interrupts should work without any problems.  The following toolkits
         are supported:  wxPython, PyQt4, PyGTK, Tk and Cocoa (OSX)::
 
             %gui wx      # enable wxPython event loop integration
             %gui qt4|qt  # enable PyQt4 event loop integration
             %gui qt5     # enable PyQt5 event loop integration
             %gui gtk     # enable PyGTK event loop integration
             %gui gtk3    # enable Gtk3 event loop integration
             %gui tk      # enable Tk event loop integration
             %gui osx     # enable Cocoa event loop integration
                          # (requires %matplotlib 1.1)
             %gui         # disable all event loop integration
 
         WARNING:  after any of these has been called you can simply create
         an application object, but DO NOT start the event loop yourself, as
         we have already handled that.
         """
         opts, arg = self.parse_options(parameter_s, '')
         if arg=='': arg = None
         try:
             return self.shell.enable_gui(arg)
         except Exception as e:
             # print simple error message, rather than traceback if we can't
             # hook up the GUI
             error(str(e))
 
     @skip_doctest
     @line_magic
     def precision(self, s=''):
         """Set floating point precision for pretty printing.
 
         Can set either integer precision or a format string.
 
         If numpy has been imported and precision is an int,
         numpy display precision will also be set, via ``numpy.set_printoptions``.
 
         If no argument is given, defaults will be restored.
 
         Examples
         --------
         ::
 
             In [1]: from math import pi
 
             In [2]: %precision 3
             Out[2]: u'%.3f'
 
             In [3]: pi
             Out[3]: 3.142
 
             In [4]: %precision %i
             Out[4]: u'%i'
 
             In [5]: pi
             Out[5]: 3
 
             In [6]: %precision %e
             Out[6]: u'%e'
 
             In [7]: pi**10
             Out[7]: 9.364805e+04
 
             In [8]: %precision
             Out[8]: u'%r'
 
             In [9]: pi**10
             Out[9]: 93648.047476082982
         """
         ptformatter = self.shell.display_formatter.formatters['text/plain']
         ptformatter.float_precision = s
         return ptformatter.float_format
 
     @magic_arguments.magic_arguments()
     @magic_arguments.argument(
         '-e', '--export', action='store_true', default=False,
         help='Export IPython history as a notebook. The filename argument '
              'is used to specify the notebook name and format. For example '
              'a filename of notebook.ipynb will result in a notebook name '
              'of "notebook" and a format of "json". Likewise using a ".py" '
              'file extension will write the notebook as a Python script'
     )
     @magic_arguments.argument(
         'filename', type=unicode_type,
         help='Notebook name or filename'
     )
     @line_magic
     def notebook(self, s):
         """Export and convert IPython notebooks.
 
         This function can export the current IPython history to a notebook file.
         For example, to export the history to "foo.ipynb" do "%notebook -e foo.ipynb".
         To export the history to "foo.py" do "%notebook -e foo.py".
         """
         args = magic_arguments.parse_argstring(self.notebook, s)
 
         from nbformat import write, v4
         args.filename = unquote_filename(args.filename)
         if args.export:
             cells = []
             hist = list(self.shell.history_manager.get_range())
             if(len(hist)<=1):
                 raise ValueError('History is empty, cannot export')
             for session, execution_count, source in hist[:-1]:
                 cells.append(v4.new_code_cell(
                     execution_count=execution_count,
                     source=source
                 ))
             nb = v4.new_notebook(cells=cells)
             with io.open(args.filename, 'w', encoding='utf-8') as f:
                 write(nb, f, version=4)