added %matplotlib --list so backends are easily visible

IPython/core/magics/pylab.py

@@ -1,155 +1,163 b''
 """Implementation of magic functions for matplotlib/pylab support.
 """
 from __future__ import print_function
 #-----------------------------------------------------------------------------
 #  Copyright (c) 2012 The IPython Development Team.
 #
 #  Distributed under the terms of the Modified BSD License.
 #
 #  The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 # Our own packages
 from traitlets.config.application import Application
 from IPython.core import magic_arguments
 from IPython.core.magic import Magics, magics_class, line_magic
 from IPython.testing.skipdoctest import skip_doctest
 from IPython.utils.warn import warn
 from IPython.core.pylabtools import backends
 
 #-----------------------------------------------------------------------------
 # Magic implementation classes
 #-----------------------------------------------------------------------------
 
 magic_gui_arg = magic_arguments.argument(
         'gui', nargs='?',
         help="""Name of the matplotlib backend to use %s.
         If given, the corresponding matplotlib backend is used,
         otherwise it will be matplotlib's default
         (which you can set in your matplotlib config file).
         """ % str(tuple(sorted(backends.keys())))
 )
 
 
 @magics_class
 class PylabMagics(Magics):
     """Magics related to matplotlib's pylab support"""
     
     @skip_doctest
     @line_magic
     @magic_arguments.magic_arguments()
+    @magic_arguments.argument('-l', '--list', default=None, action='store_true',
+                              help='Show available matplotlib backends')
     @magic_gui_arg
     def matplotlib(self, line=''):
         """Set up matplotlib to work interactively.
         
         This function lets you activate matplotlib interactive support
         at any point during an IPython session. It does not import anything
         into the interactive namespace.
         
         If you are using the inline matplotlib backend in the IPython Notebook
         you can set which figure formats are enabled using the following::
         
             In [1]: from IPython.display import set_matplotlib_formats
             
             In [2]: set_matplotlib_formats('pdf', 'svg')
 
         The default for inline figures sets `bbox_inches` to 'tight'. This can
         cause discrepancies between the displayed image and the identical
         image created using `savefig`. This behavior can be disabled using the
         `%config` magic::
             
             In [3]: %config InlineBackend.print_figure_kwargs = {'bbox_inches':None}
 
         In addition, see the docstring of
         `IPython.display.set_matplotlib_formats` and
         `IPython.display.set_matplotlib_close` for more information on
         changing additional behaviors of the inline backend.
 
         Examples
         --------
         To enable the inline backend for usage with the IPython Notebook::
         
             In [1]: %matplotlib inline
 
         In this case, where the matplotlib default is TkAgg::
 
             In [2]: %matplotlib
             Using matplotlib backend: TkAgg
 
         But you can explicitly request a different GUI backend::
 
             In [3]: %matplotlib qt
         """
+
         args = magic_arguments.parse_argstring(self.matplotlib, line)
-        gui, backend = self.shell.enable_matplotlib(args.gui)
-        self._show_matplotlib_backend(args.gui, backend)
+
+        if args.list is not None:
+            backends_list = list(backends.keys())
+            print("Available matplotlib backends: %s" % backends_list)
+        else:
+            gui, backend = self.shell.enable_matplotlib(args.gui)
+            self._show_matplotlib_backend(args.gui, backend)
 
     @skip_doctest
     @line_magic
     @magic_arguments.magic_arguments()
     @magic_arguments.argument(
         '--no-import-all', action='store_true', default=None,
         help="""Prevent IPython from performing ``import *`` into the interactive namespace.
         
         You can govern the default behavior of this flag with the
         InteractiveShellApp.pylab_import_all configurable.
         """
     )
     @magic_gui_arg
     def pylab(self, line=''):
         """Load numpy and matplotlib to work interactively.
 
         This function lets you activate pylab (matplotlib, numpy and
         interactive support) at any point during an IPython session.
         
         %pylab makes the following imports::
         
             import numpy
             import matplotlib
             from matplotlib import pylab, mlab, pyplot
             np = numpy
             plt = pyplot
             
             from IPython.display import display
             from IPython.core.pylabtools import figsize, getfigs
             
             from pylab import *
             from numpy import *
 
         If you pass `--no-import-all`, the last two `*` imports will be excluded.
         
         See the %matplotlib magic for more details about activating matplotlib
         without affecting the interactive namespace.
         """
         args = magic_arguments.parse_argstring(self.pylab, line)
         if args.no_import_all is None:
             # get default from Application
             if Application.initialized():
                 app = Application.instance()
                 try:
                     import_all = app.pylab_import_all
                 except AttributeError:
                     import_all = True
             else:
                 # nothing specified, no app - default True
                 import_all = True
         else:
             # invert no-import flag
             import_all = not args.no_import_all
 
         gui, backend, clobbered = self.shell.enable_pylab(args.gui, import_all=import_all)
         self._show_matplotlib_backend(args.gui, backend)
         print ("Populating the interactive namespace from numpy and matplotlib")
         if clobbered:
             warn("pylab import has clobbered these variables: %s"  % clobbered +
             "\n`%matplotlib` prevents importing * from pylab and numpy"
             )
     
     def _show_matplotlib_backend(self, gui, backend):
         """show matplotlib message backend message"""
         if not gui or gui == 'auto':
             print("Using matplotlib backend: %s" % backend)