Backport PR #9952: Some mpl backends have no corresponding GUI

Hopefully fixes a test failure on Windows where mpl tries to activate an `agg` gui.

Should we manually define the backend2gui dict instead of inverting backends and then modifying it?

Test failure:

```
Traceback (most recent call last):
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\unittest\case.py", line 58, in testPartExecutor
    yield
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\unittest\case.py", line 600, in run
    testMethod()
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\site-packages\nose\failure.py", line 39, in runTest
    raise self.exc_val.with_traceback(self.tb)
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\site-packages\nose\loader.py", line 418, in loadTestsFromName
    addr.filename, addr.module)
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\site-packages\nose\importer.py", line 47, in importFromPath
    return self.importFromDir(dir_path, fqname)
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\site-packages\nose\importer.py", line 94, in importFromDir
    mod = load_module(part_fqname, fh, filename, desc)
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\imp.py", line 234, in load_module
    return load_source(name, filename, file)
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\imp.py", line 172, in load_source
    module = _load(spec)
  File "<frozen importlib._bootstrap>", line 693, in _load
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 665, in exec_module
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "c:\jenkins\workspace\windows-multi\_pyversion\3.5\label\windows\IPython\core\tests\test_pylabtools.py", line 18, in <module>
    from matplotlib import pyplot as plt
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\site-packages\matplotlib\pyplot.py", line 2512, in <module>
    install_repl_displayhook()
  File "C:\Users\ADMINI~1\AppData\Local\Temp\2\1845\lib\site-packages\matplotlib\pyplot.py", line 165, in install_repl_displayhook
    ip.enable_gui(ipython_gui_name)
  File "c:\jenkins\workspace\windows-multi\_pyversion\3.5\label\windows\IPython\terminal\interactiveshell.py", line 463, in enable_gui
    self._inputhook = get_inputhook_func(gui)
  File "c:\jenkins\workspace\windows-multi\_pyversion\3.5\label\windows\IPython\terminal\pt_inputhooks\__init__.py", line 38, in get_inputhook_func
    raise UnknownBackend(gui)
IPython.terminal.pt_inputhooks.UnknownBackend: No event loop integration for 'agg'. Supported event loops are: qt, qt4, qt5, gtk, gtk2, gtk3, tk, wx, pyglet, glut, osx
```

Signed-off-by: Thomas Kluyver <[e-mail]>

IPython/core/pylabtools.py

@@ -1,394 +1,398 b''
 # -*- coding: utf-8 -*-
 """Pylab (matplotlib) support utilities."""
 from __future__ import print_function
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 from io import BytesIO
 
 from IPython.core.display import _pngxy
 from IPython.utils.decorators import flag_calls
 from IPython.utils import py3compat
 
 # If user specifies a GUI, that dictates the backend, otherwise we read the
 # user's mpl default from the mpl rc structure
 backends = {'tk': 'TkAgg',
             'gtk': 'GTKAgg',
             'gtk3': 'GTK3Agg',
             'wx': 'WXAgg',
             'qt': 'Qt4Agg', # qt3 not supported
             'qt4': 'Qt4Agg',
             'qt5': 'Qt5Agg',
             'osx': 'MacOSX',
             'nbagg': 'nbAgg',
             'notebook': 'nbAgg',
             'inline' : 'module://ipykernel.pylab.backend_inline'}
 
 # We also need a reverse backends2guis mapping that will properly choose which
 # GUI support to activate based on the desired matplotlib backend.  For the
 # most part it's just a reverse of the above dict, but we also need to add a
 # few others that map to the same GUI manually:
 backend2gui = dict(zip(backends.values(), backends.keys()))
 # Our tests expect backend2gui to just return 'qt'
 backend2gui['Qt4Agg'] = 'qt'
 # In the reverse mapping, there are a few extra valid matplotlib backends that
 # map to the same GUI support
 backend2gui['GTK'] = backend2gui['GTKCairo'] = 'gtk'
 backend2gui['GTK3Cairo'] = 'gtk3'
 backend2gui['WX'] = 'wx'
 backend2gui['CocoaAgg'] = 'osx'
+# And some backends that don't need GUI integration
+del backend2gui['nbAgg']
+del backend2gui['agg']
+del backend2gui['module://ipykernel.pylab.backend_inline']
 
 #-----------------------------------------------------------------------------
 # Matplotlib utilities
 #-----------------------------------------------------------------------------
 
 
 def getfigs(*fig_nums):
     """Get a list of matplotlib figures by figure numbers.
 
     If no arguments are given, all available figures are returned.  If the
     argument list contains references to invalid figures, a warning is printed
     but the function continues pasting further figures.
 
     Parameters
     ----------
     figs : tuple
         A tuple of ints giving the figure numbers of the figures to return.
     """
     from matplotlib._pylab_helpers import Gcf
     if not fig_nums:
         fig_managers = Gcf.get_all_fig_managers()
         return [fm.canvas.figure for fm in fig_managers]
     else:
         figs = []
         for num in fig_nums:
             f = Gcf.figs.get(num)
             if f is None:
                 print('Warning: figure %s not available.' % num)
             else:
                 figs.append(f.canvas.figure)
         return figs
 
 
 def figsize(sizex, sizey):
     """Set the default figure size to be [sizex, sizey].
 
     This is just an easy to remember, convenience wrapper that sets::
 
       matplotlib.rcParams['figure.figsize'] = [sizex, sizey]
     """
     import matplotlib
     matplotlib.rcParams['figure.figsize'] = [sizex, sizey]
 
 
 def print_figure(fig, fmt='png', bbox_inches='tight', **kwargs):
     """Print a figure to an image, and return the resulting file data
     
     Returned data will be bytes unless ``fmt='svg'``,
     in which case it will be unicode.
     
     Any keyword args are passed to fig.canvas.print_figure,
     such as ``quality`` or ``bbox_inches``.
     """
     from matplotlib import rcParams
     # When there's an empty figure, we shouldn't return anything, otherwise we
     # get big blank areas in the qt console.
     if not fig.axes and not fig.lines:
         return
 
     dpi = fig.dpi
     if fmt == 'retina':
         dpi = dpi * 2
         fmt = 'png'
     
     # build keyword args
     kw = dict(
         format=fmt,
         facecolor=fig.get_facecolor(),
         edgecolor=fig.get_edgecolor(),
         dpi=dpi,
         bbox_inches=bbox_inches,
     )
     # **kwargs get higher priority
     kw.update(kwargs)
     
     bytes_io = BytesIO()
     fig.canvas.print_figure(bytes_io, **kw)
     data = bytes_io.getvalue()
     if fmt == 'svg':
         data = data.decode('utf-8')
     return data
     
 def retina_figure(fig, **kwargs):
     """format a figure as a pixel-doubled (retina) PNG"""
     pngdata = print_figure(fig, fmt='retina', **kwargs)
     # Make sure that retina_figure acts just like print_figure and returns
     # None when the figure is empty.
     if pngdata is None:
         return
     w, h = _pngxy(pngdata)
     metadata = dict(width=w//2, height=h//2)
     return pngdata, metadata
 
 # We need a little factory function here to create the closure where
 # safe_execfile can live.
 def mpl_runner(safe_execfile):
     """Factory to return a matplotlib-enabled runner for %run.
 
     Parameters
     ----------
     safe_execfile : function
       This must be a function with the same interface as the
       :meth:`safe_execfile` method of IPython.
 
     Returns
     -------
     A function suitable for use as the ``runner`` argument of the %run magic
     function.
     """
     
     def mpl_execfile(fname,*where,**kw):
         """matplotlib-aware wrapper around safe_execfile.
 
         Its interface is identical to that of the :func:`execfile` builtin.
 
         This is ultimately a call to execfile(), but wrapped in safeties to
         properly handle interactive rendering."""
 
         import matplotlib
         import matplotlib.pylab as pylab
 
         #print '*** Matplotlib runner ***' # dbg
         # turn off rendering until end of script
         is_interactive = matplotlib.rcParams['interactive']
         matplotlib.interactive(False)
         safe_execfile(fname,*where,**kw)
         matplotlib.interactive(is_interactive)
         # make rendering call now, if the user tried to do it
         if pylab.draw_if_interactive.called:
             pylab.draw()
             pylab.draw_if_interactive.called = False
 
     return mpl_execfile
 
 
 def _reshow_nbagg_figure(fig):
     """reshow an nbagg figure"""
     try:
         reshow = fig.canvas.manager.reshow
     except AttributeError:
         raise NotImplementedError()
     else:
         reshow()
 
 
 def select_figure_formats(shell, formats, **kwargs):
     """Select figure formats for the inline backend.
 
     Parameters
     ==========
     shell : InteractiveShell
         The main IPython instance.
     formats : str or set
         One or a set of figure formats to enable: 'png', 'retina', 'jpeg', 'svg', 'pdf'.
     **kwargs : any
         Extra keyword arguments to be passed to fig.canvas.print_figure.
     """
     import matplotlib
     from matplotlib.figure import Figure
 
     svg_formatter = shell.display_formatter.formatters['image/svg+xml']
     png_formatter = shell.display_formatter.formatters['image/png']
     jpg_formatter = shell.display_formatter.formatters['image/jpeg']
     pdf_formatter = shell.display_formatter.formatters['application/pdf']
 
     if isinstance(formats, py3compat.string_types):
         formats = {formats}
     # cast in case of list / tuple
     formats = set(formats)
 
     [ f.pop(Figure, None) for f in shell.display_formatter.formatters.values() ]
 
     if matplotlib.get_backend().lower() == 'nbagg':
         formatter = shell.display_formatter.ipython_display_formatter
         formatter.for_type(Figure, _reshow_nbagg_figure)
 
     supported = {'png', 'png2x', 'retina', 'jpg', 'jpeg', 'svg', 'pdf'}
     bad = formats.difference(supported)
     if bad:
         bs = "%s" % ','.join([repr(f) for f in bad])
         gs = "%s" % ','.join([repr(f) for f in supported])
         raise ValueError("supported formats are: %s not %s" % (gs, bs))
     
     if 'png' in formats:
         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
     if 'retina' in formats or 'png2x' in formats:
         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))
     if 'jpg' in formats or 'jpeg' in formats:
         jpg_formatter.for_type(Figure, lambda fig: print_figure(fig, 'jpg', **kwargs))
     if 'svg' in formats:
         svg_formatter.for_type(Figure, lambda fig: print_figure(fig, 'svg', **kwargs))
     if 'pdf' in formats:
         pdf_formatter.for_type(Figure, lambda fig: print_figure(fig, 'pdf', **kwargs))
 
 #-----------------------------------------------------------------------------
 # Code for initializing matplotlib and importing pylab
 #-----------------------------------------------------------------------------
 
 
 def find_gui_and_backend(gui=None, gui_select=None):
     """Given a gui string return the gui and mpl backend.
 
     Parameters
     ----------
     gui : str
         Can be one of ('tk','gtk','wx','qt','qt4','inline').
     gui_select : str
         Can be one of ('tk','gtk','wx','qt','qt4','inline').
         This is any gui already selected by the shell.
 
     Returns
     -------
     A tuple of (gui, backend) where backend is one of ('TkAgg','GTKAgg',
     'WXAgg','Qt4Agg','module://ipykernel.pylab.backend_inline').
     """
 
     import matplotlib
 
     if gui and gui != 'auto':
         # select backend based on requested gui
         backend = backends[gui]
     else:
         # We need to read the backend from the original data structure, *not*
         # from mpl.rcParams, since a prior invocation of %matplotlib may have
         # overwritten that.
         # WARNING: this assumes matplotlib 1.1 or newer!!
         backend = matplotlib.rcParamsOrig['backend']
         # In this case, we need to find what the appropriate gui selection call
         # should be for IPython, so we can activate inputhook accordingly
         gui = backend2gui.get(backend, None)
 
         # If we have already had a gui active, we need it and inline are the
         # ones allowed.
         if gui_select and gui != gui_select:
             gui = gui_select
             backend = backends[gui]
 
     return gui, backend
 
 
 def activate_matplotlib(backend):
     """Activate the given backend and set interactive to True."""
 
     import matplotlib
     matplotlib.interactive(True)
     
     # Matplotlib had a bug where even switch_backend could not force
     # the rcParam to update. This needs to be set *before* the module
     # magic of switch_backend().
     matplotlib.rcParams['backend'] = backend
 
     import matplotlib.pyplot
     matplotlib.pyplot.switch_backend(backend)
 
     # This must be imported last in the matplotlib series, after
     # backend/interactivity choices have been made
     import matplotlib.pylab as pylab
 
     pylab.show._needmain = False
     # We need to detect at runtime whether show() is called by the user.
     # For this, we wrap it into a decorator which adds a 'called' flag.
     pylab.draw_if_interactive = flag_calls(pylab.draw_if_interactive)
 
 
 def import_pylab(user_ns, import_all=True):
     """Populate the namespace with pylab-related values.
     
     Imports matplotlib, pylab, numpy, and everything from pylab and numpy.
     
     Also imports a few names from IPython (figsize, display, getfigs)
     
     """
 
     # Import numpy as np/pyplot as plt are conventions we're trying to
     # somewhat standardize on.  Making them available to users by default
     # will greatly help this.
     s = ("import numpy\n"
           "import matplotlib\n"
           "from matplotlib import pylab, mlab, pyplot\n"
           "np = numpy\n"
           "plt = pyplot\n"
           )
     exec(s, user_ns)
     
     if import_all:
         s = ("from matplotlib.pylab import *\n"
              "from numpy import *\n")
         exec(s, user_ns)
     
     # IPython symbols to add
     user_ns['figsize'] = figsize
     from IPython.core.display import display
     # Add display and getfigs to the user's namespace
     user_ns['display'] = display
     user_ns['getfigs'] = getfigs
 
 
 def configure_inline_support(shell, backend):
     """Configure an IPython shell object for matplotlib use.
 
     Parameters
     ----------
     shell : InteractiveShell instance
 
     backend : matplotlib backend
     """
     # If using our svg payload backend, register the post-execution
     # function that will pick up the results for display.  This can only be
     # done with access to the real shell object.
 
     # Note: if we can't load the inline backend, then there's no point
     # continuing (such as in terminal-only shells in environments without
     # zeromq available).
     try:
         from ipykernel.pylab.backend_inline import InlineBackend
     except ImportError:
         return
     import matplotlib
 
     cfg = InlineBackend.instance(parent=shell)
     cfg.shell = shell
     if cfg not in shell.configurables:
         shell.configurables.append(cfg)
 
     if backend == backends['inline']:
         from ipykernel.pylab.backend_inline import flush_figures
         shell.events.register('post_execute', flush_figures)
 
         # Save rcParams that will be overwrittern
         shell._saved_rcParams = dict()
         for k in cfg.rc:
             shell._saved_rcParams[k] = matplotlib.rcParams[k]
         # load inline_rc
         matplotlib.rcParams.update(cfg.rc)
         new_backend_name = "inline"
     else:
         from ipykernel.pylab.backend_inline import flush_figures
         try:
             shell.events.unregister('post_execute', flush_figures)
         except ValueError:
             pass
         if hasattr(shell, '_saved_rcParams'):
             matplotlib.rcParams.update(shell._saved_rcParams)
             del shell._saved_rcParams
         new_backend_name = "other"
 
     # only enable the formats once -> don't change the enabled formats (which the user may
     # has changed) when getting another "%matplotlib inline" call.
     # See https://github.com/ipython/ipykernel/issues/29
     cur_backend = getattr(configure_inline_support, "current_backend", "unset")
     if new_backend_name != cur_backend:
         # Setup the default figure format
         select_figure_formats(shell, cfg.figure_formats, **cfg.print_figure_kwargs)
         configure_inline_support.current_backend = new_backend_name