Correctly handle "ipython --matplotlib=<whatever>"

IPython/core/magics/pylab.py

@@ -1,178 +1,173 b''
 """Implementation of magic functions for matplotlib/pylab support.
 """
 #-----------------------------------------------------------------------------
 #  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 warnings import warn
 
 #-----------------------------------------------------------------------------
 # Magic implementation classes
 #-----------------------------------------------------------------------------
 
 magic_gui_arg = magic_arguments.argument(
     "gui",
     nargs="?",
     help="""Name of the matplotlib backend to use such as 'qt' or 'widget'.
         If given, the corresponding matplotlib backend is used,
         otherwise it will be matplotlib's default
         (which you can set in your matplotlib config file).
         """,
 )
 
 
 @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', 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 matplotlib_inline.backend_inline 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 docstrings of
         `matplotlib_inline.backend_inline.set_matplotlib_formats` and
         `matplotlib_inline.backend_inline.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
 
         You can list the available backends using the -l/--list option::
 
            In [4]: %matplotlib --list
            Available matplotlib backends: ['osx', 'qt4', 'qt5', 'gtk3', 'gtk4', 'notebook', 'wx', 'qt', 'nbagg',
            'gtk', 'tk', 'inline']
         """
         args = magic_arguments.parse_argstring(self.matplotlib, line)
         if args.list:
-            from IPython.core.pylabtools import _matplotlib_manages_backends
+            from IPython.core.pylabtools import _list_matplotlib_backends_and_gui_loops
 
-            if _matplotlib_manages_backends():
-                from matplotlib.backends.registry import backend_registry
-
-                backends_list = backend_registry.list_all()
-            else:
-                from IPython.core.pylabtools import backends
-
-                backends_list = list(backends.keys())
-            print("Available matplotlib backends: %s" % backends_list)
+            print(
+                "Available matplotlib backends: %s"
+                % _list_matplotlib_backends_and_gui_loops()
+            )
         else:
             gui, backend = self.shell.enable_matplotlib(args.gui.lower() if isinstance(args.gui, str) else 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(
             "%pylab is deprecated, use %matplotlib inline and import the required libraries."
         )
         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)

IPython/core/pylabtools.py

@@ -1,499 +1,518 b''
 # -*- coding: utf-8 -*-
 """Pylab (matplotlib) support utilities."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 from io import BytesIO
 from binascii import b2a_base64
 from functools import partial
 import warnings
 
 from IPython.core.display import _pngxy
 from IPython.utils.decorators import flag_calls
 
 
 # Matplotlib backend resolution functionality moved from IPython to Matplotlib
 # in IPython 8.24 and Matplotlib 3.9.1. Need to keep `backends` and `backend2gui`
 # here for earlier Matplotlib and for external backend libraries such as
 # mplcairo that might rely upon it.
 _deprecated_backends = {
     "tk": "TkAgg",
     "gtk": "GTKAgg",
     "gtk3": "GTK3Agg",
     "gtk4": "GTK4Agg",
     "wx": "WXAgg",
     "qt4": "Qt4Agg",
     "qt5": "Qt5Agg",
     "qt6": "QtAgg",
     "qt": "QtAgg",
     "osx": "MacOSX",
     "nbagg": "nbAgg",
     "webagg": "WebAgg",
     "notebook": "nbAgg",
     "agg": "agg",
     "svg": "svg",
     "pdf": "pdf",
     "ps": "ps",
     "inline": "module://matplotlib_inline.backend_inline",
     "ipympl": "module://ipympl.backend_nbagg",
     "widget": "module://ipympl.backend_nbagg",
 }
 
 # 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:
 _deprecated_backend2gui = dict(
     zip(_deprecated_backends.values(), _deprecated_backends.keys())
 )
 # In the reverse mapping, there are a few extra valid matplotlib backends that
 # map to the same GUI support
 _deprecated_backend2gui["GTK"] = _deprecated_backend2gui["GTKCairo"] = "gtk"
 _deprecated_backend2gui["GTK3Cairo"] = "gtk3"
 _deprecated_backend2gui["GTK4Cairo"] = "gtk4"
 _deprecated_backend2gui["WX"] = "wx"
 _deprecated_backend2gui["CocoaAgg"] = "osx"
 # There needs to be a hysteresis here as the new QtAgg Matplotlib backend
 # supports either Qt5 or Qt6 and the IPython qt event loop support Qt4, Qt5,
 # and Qt6.
 _deprecated_backend2gui["QtAgg"] = "qt"
 _deprecated_backend2gui["Qt4Agg"] = "qt4"
 _deprecated_backend2gui["Qt5Agg"] = "qt5"
 
 # And some backends that don't need GUI integration
 del _deprecated_backend2gui["nbAgg"]
 del _deprecated_backend2gui["agg"]
 del _deprecated_backend2gui["svg"]
 del _deprecated_backend2gui["pdf"]
 del _deprecated_backend2gui["ps"]
 del _deprecated_backend2gui["module://matplotlib_inline.backend_inline"]
 del _deprecated_backend2gui["module://ipympl.backend_nbagg"]
 
 
 # Deprecated attributes backends and backend2gui mostly following PEP 562.
 def __getattr__(name):
     if name in ("backends", "backend2gui"):
         warnings.warn(
             f"{name} is deprecated since IPython 8.24, backends are managed "
             "in matplotlib and can be externally registered.",
             DeprecationWarning,
         )
         return globals()[f"_deprecated_{name}"]
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
 
 
 #-----------------------------------------------------------------------------
 # 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", base64=False, **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``.
 
     If `base64` is True, return base64-encoded str instead of raw bytes
     for binary-encoded image formats
 
     .. versionadded:: 7.29
         base64 argument
     """
     # 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 = {
         "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()
     if fig.canvas is None:
         from matplotlib.backend_bases import FigureCanvasBase
         FigureCanvasBase(fig)
 
     fig.canvas.print_figure(bytes_io, **kw)
     data = bytes_io.getvalue()
     if fmt == 'svg':
         data = data.decode('utf-8')
     elif base64:
         data = b2a_base64(data, newline=False).decode("ascii")
     return data
 
 def retina_figure(fig, base64=False, **kwargs):
     """format a figure as a pixel-doubled (retina) PNG
 
     If `base64` is True, return base64-encoded str instead of raw bytes
     for binary-encoded image formats
 
     .. versionadded:: 7.29
         base64 argument
     """
     pngdata = print_figure(fig, fmt="retina", base64=False, **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 = {"width": w//2, "height":h//2}
     if base64:
         pngdata = b2a_base64(pngdata, newline=False).decode("ascii")
     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.pyplot as plt
 
         #print '*** Matplotlib runner ***' # dbg
         # turn off rendering until end of script
         with matplotlib.rc_context({"interactive": False}):
             safe_execfile(fname, *where, **kw)
 
         if matplotlib.is_interactive():
             plt.show()
 
         # make rendering call now, if the user tried to do it
         if plt.draw_if_interactive.called:
             plt.draw()
             plt.draw_if_interactive.called = False
 
         # re-draw everything that is stale
         try:
             da = plt.draw_all
         except AttributeError:
             pass
         else:
             da()
 
     return mpl_execfile
 
 
 def _reshow_nbagg_figure(fig):
     """reshow an nbagg figure"""
     try:
         reshow = fig.canvas.manager.reshow
     except AttributeError as e:
         raise NotImplementedError() from e
     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, str):
         formats = {formats}
     # cast in case of list / tuple
     formats = set(formats)
 
     [ f.pop(Figure, None) for f in shell.display_formatter.formatters.values() ]
     mplbackend = matplotlib.get_backend().lower()
     if mplbackend in ("nbagg", "ipympl", "widget", "module://ipympl.backend_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, partial(print_figure, fmt="png", base64=True, **kwargs)
         )
     if "retina" in formats or "png2x" in formats:
         png_formatter.for_type(Figure, partial(retina_figure, base64=True, **kwargs))
     if "jpg" in formats or "jpeg" in formats:
         jpg_formatter.for_type(
             Figure, partial(print_figure, fmt="jpg", base64=True, **kwargs)
         )
     if "svg" in formats:
         svg_formatter.for_type(Figure, partial(print_figure, fmt="svg", **kwargs))
     if "pdf" in formats:
         pdf_formatter.for_type(
             Figure, partial(print_figure, fmt="pdf", base64=True, **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','agg').
     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://matplotlib_inline.backend_inline','agg').
     """
 
     import matplotlib
 
     if _matplotlib_manages_backends():
         backend_registry = matplotlib.backends.registry.backend_registry
 
         # gui argument may be a gui event loop or may be a backend name.
         if gui in ("auto", None):
             backend = matplotlib.rcParamsOrig["backend"]
             backend, gui = backend_registry.resolve_backend(backend)
         else:
             backend, gui = backend_registry.resolve_gui_or_backend(gui)
 
         return gui, backend
 
     # Fallback to previous behaviour (Matplotlib < 3.9)
     mpl_version_info = getattr(matplotlib, "__version_info__", (0, 0))
     has_unified_qt_backend = mpl_version_info >= (3, 5)
 
     from IPython.core.pylabtools import backends
 
     backends_ = dict(backends)
     if not has_unified_qt_backend:
         backends_["qt"] = "qt5agg"
 
     if gui and gui != 'auto':
         # select backend based on requested gui
         backend = backends_[gui]
         if gui == 'agg':
             gui = None
     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
         from IPython.core.pylabtools import backend2gui
         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]
 
     # Matplotlib before _matplotlib_manages_backends() can return "inline" for
     # no gui event loop rather than the None that IPython >= 8.24.0 expects.
     if gui == "inline":
         gui = None
 
     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
 
     # Due to circular imports, pyplot may be only partially initialised
     # when this function runs.
     # So avoid needing matplotlib attribute-lookup to access pyplot.
     from matplotlib import pyplot as plt
 
     plt.switch_backend(backend)
 
     plt.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.
     plt.draw_if_interactive = flag_calls(plt.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.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):
     """
     .. deprecated:: 7.23
 
         use `matplotlib_inline.backend_inline.configure_inline_support()`
 
     Configure an IPython shell object for matplotlib use.
 
     Parameters
     ----------
     shell : InteractiveShell instance
     backend : matplotlib backend
     """
     warnings.warn(
         "`configure_inline_support` is deprecated since IPython 7.23, directly "
         "use `matplotlib_inline.backend_inline.configure_inline_support()`",
         DeprecationWarning,
         stacklevel=2,
     )
 
     from matplotlib_inline.backend_inline import (
         configure_inline_support as configure_inline_support_orig,
     )
 
     configure_inline_support_orig(shell, backend)
 
 
 # Determine if Matplotlib manages backends only if needed, and cache result.
 # Do not read this directly, instead use _matplotlib_manages_backends().
 _matplotlib_manages_backends_value: bool | None = None
 
 
 def _matplotlib_manages_backends() -> bool:
     """Return True if Matplotlib manages backends, False otherwise.
 
     If it returns True, the caller can be sure that
     matplotlib.backends.registry.backend_registry is available along with
-    member functions resolve_gui_or_backend, resolve_backend and list_all.
+    member functions resolve_gui_or_backend, resolve_backend, list_all, and
+    list_gui_frameworks.
     """
     global _matplotlib_manages_backends_value
     if _matplotlib_manages_backends_value is None:
         try:
             from matplotlib.backends.registry import backend_registry
 
             _matplotlib_manages_backends_value = hasattr(
                 backend_registry, "resolve_gui_or_backend"
             )
         except ImportError:
             _matplotlib_manages_backends_value = False
 
     return _matplotlib_manages_backends_value
+
+
+def _list_matplotlib_backends_and_gui_loops() -> list[str]:
+    """Return list of all Matplotlib backends and GUI event loops.
+
+    This is the list returned by
+        %matplotlib --list
+    """
+    if _matplotlib_manages_backends():
+        from matplotlib.backends.registry import backend_registry
+
+        ret = backend_registry.list_all() + backend_registry.list_gui_frameworks()
+    else:
+        from IPython.core import pylabtools
+
+        ret = list(pylabtools.backends.keys())
+
+    return sorted(["auto"] + ret)

IPython/core/shellapp.py

@@ -1,450 +1,491 b''
 # encoding: utf-8
 """
 A mixin for :class:`~IPython.core.application.Application` classes that
 launch InteractiveShell instances, load extensions, etc.
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import glob
 from itertools import chain
 import os
 import sys
+import typing as t
 
 from traitlets.config.application import boolean_flag
 from traitlets.config.configurable import Configurable
 from traitlets.config.loader import Config
 from IPython.core.application import SYSTEM_CONFIG_DIRS, ENV_CONFIG_DIRS
-from IPython.core import pylabtools
 from IPython.utils.contexts import preserve_keys
 from IPython.utils.path import filefind
 from traitlets import (
-    Unicode, Instance, List, Bool, CaselessStrEnum, observe,
+    Unicode,
+    Instance,
+    List,
+    Bool,
+    CaselessStrEnum,
+    observe,
     DottedObjectName,
+    Undefined,
 )
 from IPython.terminal import pt_inputhooks
 
 #-----------------------------------------------------------------------------
 # Aliases and Flags
 #-----------------------------------------------------------------------------
 
 gui_keys = tuple(sorted(pt_inputhooks.backends) + sorted(pt_inputhooks.aliases))
 
-backend_keys: list[str] = []
-
 shell_flags = {}
 
 addflag = lambda *args: shell_flags.update(boolean_flag(*args))
-addflag('autoindent', 'InteractiveShell.autoindent',
-        'Turn on autoindenting.', 'Turn off autoindenting.'
+addflag(
+    "autoindent",
+    "InteractiveShell.autoindent",
+    "Turn on autoindenting.",
+    "Turn off autoindenting.",
 )
-addflag('automagic', 'InteractiveShell.automagic',
+addflag(
+    "automagic",
+    "InteractiveShell.automagic",
         """Turn on the auto calling of magic commands. Type %%magic at the
         IPython  prompt  for  more information.""",
         'Turn off the auto calling of magic commands.'
 )
 addflag('pdb', 'InteractiveShell.pdb',
     "Enable auto calling the pdb debugger after every exception.",
     "Disable auto calling the pdb debugger after every exception."
 )
 addflag('pprint', 'PlainTextFormatter.pprint',
     "Enable auto pretty printing of results.",
     "Disable auto pretty printing of results."
 )
 addflag('color-info', 'InteractiveShell.color_info',
     """IPython can display information about objects via a set of functions,
     and optionally can use colors for this, syntax highlighting
     source code and various other elements. This is on by default, but can cause
     problems with some pagers. If you see such problems, you can disable the
     colours.""",
     "Disable using colors for info related things."
 )
 addflag('ignore-cwd', 'InteractiveShellApp.ignore_cwd',
         "Exclude the current working directory from sys.path",
         "Include the current working directory in sys.path",
 )
 nosep_config = Config()
 nosep_config.InteractiveShell.separate_in = ''
 nosep_config.InteractiveShell.separate_out = ''
 nosep_config.InteractiveShell.separate_out2 = ''
 
 shell_flags['nosep']=(nosep_config, "Eliminate all spacing between prompts.")
 shell_flags['pylab'] = (
     {'InteractiveShellApp' : {'pylab' : 'auto'}},
     """Pre-load matplotlib and numpy for interactive use with
     the default matplotlib backend."""
 )
 shell_flags['matplotlib'] = (
     {'InteractiveShellApp' : {'matplotlib' : 'auto'}},
     """Configure matplotlib for interactive use with
     the default matplotlib backend."""
 )
 
 # it's possible we don't want short aliases for *all* of these:
 shell_aliases = dict(
     autocall='InteractiveShell.autocall',
     colors='InteractiveShell.colors',
     logfile='InteractiveShell.logfile',
     logappend='InteractiveShell.logappend',
     c='InteractiveShellApp.code_to_run',
     m='InteractiveShellApp.module_to_run',
     ext="InteractiveShellApp.extra_extensions",
     gui='InteractiveShellApp.gui',
     pylab='InteractiveShellApp.pylab',
     matplotlib='InteractiveShellApp.matplotlib',
 )
 shell_aliases['cache-size'] = 'InteractiveShell.cache_size'
 
+
+# -----------------------------------------------------------------------------
+# Traitlets
+# -----------------------------------------------------------------------------
+
+
+class MatplotlibBackendCaselessStrEnum(CaselessStrEnum):
+    """An enum of Matplotlib backend strings where the case should be ignored.
+
+    Prior to Matplotlib 3.9.1 the list of valid backends is hardcoded in
+    pylabtools.backends. After that, Matplotlib manages backends.
+
+    The list of valid backends is determined when it is first needed to avoid
+    wasting unnecessary initialisation time.
+    """
+
+    def __init__(
+        self: CaselessStrEnum[t.Any],
+        default_value: t.Any = Undefined,
+        **kwargs: t.Any,
+    ) -> None:
+        super().__init__(None, default_value=default_value, **kwargs)
+
+    def __getattribute__(self, name):
+        if name == "values" and object.__getattribute__(self, name) is None:
+            from IPython.core.pylabtools import _list_matplotlib_backends_and_gui_loops
+
+            self.values = _list_matplotlib_backends_and_gui_loops()
+        return object.__getattribute__(self, name)
+
+
 #-----------------------------------------------------------------------------
 # Main classes and functions
 #-----------------------------------------------------------------------------
 
 class InteractiveShellApp(Configurable):
     """A Mixin for applications that start InteractiveShell instances.
 
     Provides configurables for loading extensions and executing files
     as part of configuring a Shell environment.
 
     The following methods should be called by the :meth:`initialize` method
     of the subclass:
 
       - :meth:`init_path`
       - :meth:`init_shell` (to be implemented by the subclass)
       - :meth:`init_gui_pylab`
       - :meth:`init_extensions`
       - :meth:`init_code`
     """
     extensions = List(Unicode(),
         help="A list of dotted module names of IPython extensions to load."
     ).tag(config=True)
 
     extra_extensions = List(
         DottedObjectName(),
         help="""
         Dotted module name(s) of one or more IPython extensions to load.
 
         For specifying extra extensions to load on the command-line.
 
         .. versionadded:: 7.10
         """,
     ).tag(config=True)
 
     reraise_ipython_extension_failures = Bool(False,
         help="Reraise exceptions encountered loading IPython extensions?",
     ).tag(config=True)
 
     # Extensions that are always loaded (not configurable)
     default_extensions = List(Unicode(), [u'storemagic']).tag(config=False)
 
     hide_initial_ns = Bool(True,
         help="""Should variables loaded at startup (by startup files, exec_lines, etc.)
         be hidden from tools like %who?"""
     ).tag(config=True)
 
     exec_files = List(Unicode(),
         help="""List of files to run at IPython startup."""
     ).tag(config=True)
     exec_PYTHONSTARTUP = Bool(True,
         help="""Run the file referenced by the PYTHONSTARTUP environment
         variable at IPython startup."""
     ).tag(config=True)
     file_to_run = Unicode('',
         help="""A file to be run""").tag(config=True)
 
     exec_lines = List(Unicode(),
         help="""lines of code to run at IPython startup."""
     ).tag(config=True)
-    code_to_run = Unicode('',
-        help="Execute the given command string."
-    ).tag(config=True)
-    module_to_run = Unicode('',
-        help="Run the module as a script."
-    ).tag(config=True)
-    gui = CaselessStrEnum(gui_keys, allow_none=True,
-        help="Enable GUI event loop integration with any of {0}.".format(gui_keys)
+    code_to_run = Unicode("", help="Execute the given command string.").tag(config=True)
+    module_to_run = Unicode("", help="Run the module as a script.").tag(config=True)
+    gui = CaselessStrEnum(
+        gui_keys,
+        allow_none=True,
+        help="Enable GUI event loop integration with any of {0}.".format(gui_keys),
     ).tag(config=True)
-    matplotlib = CaselessStrEnum(backend_keys, allow_none=True,
+    matplotlib = MatplotlibBackendCaselessStrEnum(
+        allow_none=True,
         help="""Configure matplotlib for interactive use with
-        the default matplotlib backend."""
+        the default matplotlib backend.""",
     ).tag(config=True)
-    pylab = CaselessStrEnum(backend_keys, allow_none=True,
+    pylab = MatplotlibBackendCaselessStrEnum(
+        allow_none=True,
         help="""Pre-load matplotlib and numpy for interactive use,
         selecting a particular matplotlib backend and loop integration.
-        """
+        """,
     ).tag(config=True)
-    pylab_import_all = Bool(True,
+    pylab_import_all = Bool(
+        True,
         help="""If true, IPython will populate the user namespace with numpy, pylab, etc.
         and an ``import *`` is done from numpy and pylab, when using pylab mode.
 
         When False, pylab mode should not import any names into the user namespace.
-        """
+        """,
     ).tag(config=True)
     ignore_cwd = Bool(
         False,
         help="""If True, IPython will not add the current working directory to sys.path.
         When False, the current working directory is added to sys.path, allowing imports
         of modules defined in the current directory."""
     ).tag(config=True)
     shell = Instance('IPython.core.interactiveshell.InteractiveShellABC',
                      allow_none=True)
     # whether interact-loop should start
     interact = Bool(True)
 
     user_ns = Instance(dict, args=None, allow_none=True)
     @observe('user_ns')
     def _user_ns_changed(self, change):
         if self.shell is not None:
             self.shell.user_ns = change['new']
             self.shell.init_user_ns()
 
     def init_path(self):
         """Add current working directory, '', to sys.path
 
         Unlike Python's default, we insert before the first `site-packages`
         or `dist-packages` directory,
         so that it is after the standard library.
 
         .. versionchanged:: 7.2
             Try to insert after the standard library, instead of first.
         .. versionchanged:: 8.0
             Allow optionally not including the current directory in sys.path
         """
         if '' in sys.path or self.ignore_cwd:
             return
         for idx, path in enumerate(sys.path):
             parent, last_part = os.path.split(path)
             if last_part in {'site-packages', 'dist-packages'}:
                 break
         else:
             # no site-packages or dist-packages found (?!)
             # back to original behavior of inserting at the front
             idx = 0
         sys.path.insert(idx, '')
 
     def init_shell(self):
         raise NotImplementedError("Override in subclasses")
 
     def init_gui_pylab(self):
         """Enable GUI event loop integration, taking pylab into account."""
         enable = False
         shell = self.shell
         if self.pylab:
             enable = lambda key: shell.enable_pylab(key, import_all=self.pylab_import_all)
             key = self.pylab
         elif self.matplotlib:
             enable = shell.enable_matplotlib
             key = self.matplotlib
         elif self.gui:
             enable = shell.enable_gui
             key = self.gui
 
         if not enable:
             return
 
         try:
             r = enable(key)
         except ImportError:
             self.log.warning("Eventloop or matplotlib integration failed. Is matplotlib installed?")
             self.shell.showtraceback()
             return
         except Exception:
             self.log.warning("GUI event loop or pylab initialization failed")
             self.shell.showtraceback()
             return
 
         if isinstance(r, tuple):
             gui, backend = r[:2]
             self.log.info("Enabling GUI event loop integration, "
                       "eventloop=%s, matplotlib=%s", gui, backend)
             if key == "auto":
                 print("Using matplotlib backend: %s" % backend)
         else:
             gui = r
             self.log.info("Enabling GUI event loop integration, "
                       "eventloop=%s", gui)
 
     def init_extensions(self):
         """Load all IPython extensions in IPythonApp.extensions.
 
         This uses the :meth:`ExtensionManager.load_extensions` to load all
         the extensions listed in ``self.extensions``.
         """
         try:
             self.log.debug("Loading IPython extensions...")
             extensions = (
                 self.default_extensions + self.extensions + self.extra_extensions
             )
             for ext in extensions:
                 try:
                     self.log.info("Loading IPython extension: %s", ext)
                     self.shell.extension_manager.load_extension(ext)
                 except:
                     if self.reraise_ipython_extension_failures:
                         raise
                     msg = ("Error in loading extension: {ext}\n"
                            "Check your config files in {location}".format(
                                ext=ext,
                                location=self.profile_dir.location
                            ))
                     self.log.warning(msg, exc_info=True)
         except:
             if self.reraise_ipython_extension_failures:
                 raise
             self.log.warning("Unknown error in loading extensions:", exc_info=True)
 
     def init_code(self):
         """run the pre-flight code, specified via exec_lines"""
         self._run_startup_files()
         self._run_exec_lines()
         self._run_exec_files()
 
         # Hide variables defined here from %who etc.
         if self.hide_initial_ns:
             self.shell.user_ns_hidden.update(self.shell.user_ns)
 
         # command-line execution (ipython -i script.py, ipython -m module)
         # should *not* be excluded from %whos
         self._run_cmd_line_code()
         self._run_module()
 
         # flush output, so itwon't be attached to the first cell
         sys.stdout.flush()
         sys.stderr.flush()
         self.shell._sys_modules_keys = set(sys.modules.keys())
 
     def _run_exec_lines(self):
         """Run lines of code in IPythonApp.exec_lines in the user's namespace."""
         if not self.exec_lines:
             return
         try:
             self.log.debug("Running code from IPythonApp.exec_lines...")
             for line in self.exec_lines:
                 try:
                     self.log.info("Running code in user namespace: %s" %
                                   line)
                     self.shell.run_cell(line, store_history=False)
                 except:
                     self.log.warning("Error in executing line in user "
                                   "namespace: %s" % line)
                     self.shell.showtraceback()
         except:
             self.log.warning("Unknown error in handling IPythonApp.exec_lines:")
             self.shell.showtraceback()
 
     def _exec_file(self, fname, shell_futures=False):
         try:
             full_filename = filefind(fname, [u'.', self.ipython_dir])
         except IOError:
             self.log.warning("File not found: %r"%fname)
             return
         # Make sure that the running script gets a proper sys.argv as if it
         # were run from a system shell.
         save_argv = sys.argv
         sys.argv = [full_filename] + self.extra_args[1:]
         try:
             if os.path.isfile(full_filename):
                 self.log.info("Running file in user namespace: %s" %
                               full_filename)
                 # Ensure that __file__ is always defined to match Python
                 # behavior.
                 with preserve_keys(self.shell.user_ns, '__file__'):
                     self.shell.user_ns['__file__'] = fname
                     if full_filename.endswith('.ipy') or full_filename.endswith('.ipynb'):
                         self.shell.safe_execfile_ipy(full_filename,
                                                      shell_futures=shell_futures)
                     else:
                         # default to python, even without extension
                         self.shell.safe_execfile(full_filename,
                                                  self.shell.user_ns,
                                                  shell_futures=shell_futures,
                                                  raise_exceptions=True)
         finally:
             sys.argv = save_argv
 
     def _run_startup_files(self):
         """Run files from profile startup directory"""
         startup_dirs = [self.profile_dir.startup_dir] + [
             os.path.join(p, 'startup') for p in chain(ENV_CONFIG_DIRS, SYSTEM_CONFIG_DIRS)
         ]
         startup_files = []
 
         if self.exec_PYTHONSTARTUP and os.environ.get('PYTHONSTARTUP', False) and \
                 not (self.file_to_run or self.code_to_run or self.module_to_run):
             python_startup = os.environ['PYTHONSTARTUP']
             self.log.debug("Running PYTHONSTARTUP file %s...", python_startup)
             try:
                 self._exec_file(python_startup)
             except:
                 self.log.warning("Unknown error in handling PYTHONSTARTUP file %s:", python_startup)
                 self.shell.showtraceback()
         for startup_dir in startup_dirs[::-1]:
             startup_files += glob.glob(os.path.join(startup_dir, '*.py'))
             startup_files += glob.glob(os.path.join(startup_dir, '*.ipy'))
         if not startup_files:
             return
 
         self.log.debug("Running startup files from %s...", startup_dir)
         try:
             for fname in sorted(startup_files):
                 self._exec_file(fname)
         except:
             self.log.warning("Unknown error in handling startup files:")
             self.shell.showtraceback()
 
     def _run_exec_files(self):
         """Run files from IPythonApp.exec_files"""
         if not self.exec_files:
             return
 
         self.log.debug("Running files in IPythonApp.exec_files...")
         try:
             for fname in self.exec_files:
                 self._exec_file(fname)
         except:
             self.log.warning("Unknown error in handling IPythonApp.exec_files:")
             self.shell.showtraceback()
 
     def _run_cmd_line_code(self):
         """Run code or file specified at the command-line"""
         if self.code_to_run:
             line = self.code_to_run
             try:
                 self.log.info("Running code given at command line (c=): %s" %
                               line)
                 self.shell.run_cell(line, store_history=False)
             except:
                 self.log.warning("Error in executing line in user namespace: %s" %
                               line)
                 self.shell.showtraceback()
                 if not self.interact:
                     self.exit(1)
 
         # Like Python itself, ignore the second if the first of these is present
         elif self.file_to_run:
             fname = self.file_to_run
             if os.path.isdir(fname):
                 fname = os.path.join(fname, "__main__.py")
             if not os.path.exists(fname):
                 self.log.warning("File '%s' doesn't exist", fname)
                 if not self.interact:
                     self.exit(2)
             try:
                 self._exec_file(fname, shell_futures=True)
             except:
                 self.shell.showtraceback(tb_offset=4)
                 if not self.interact:
                     self.exit(1)
 
     def _run_module(self):
         """Run module specified at the command-line."""
         if self.module_to_run:
             # Make sure that the module gets a proper sys.argv as if it were
             # run using `python -m`.
             save_argv = sys.argv
             sys.argv = [sys.executable] + self.extra_args
             try:
                 self.shell.safe_run_module(self.module_to_run,
                                            self.shell.user_ns)
             finally:
                 sys.argv = save_argv