Don't force matplotlib backend names to be lowercase (#14475)

This is something I missed as part of moving the backend resolution to
Matplotlib. Since version 3.9.0 Matplotlib handles the case-sensitivity
of backend names, making them all lowercase for internal use. But since
matplotlib/matplotlib#28473 uppercase letters are allowed in backend
names of the form `module://soMe_moDule.sOmE_NAme`. Hence we need to not
force backend names to be lowercase in IPython when passing them to
Matplotlib. It is just a one line change that happens to make the code
simpler, plus a new test.

The Matplotlib change will be released in 3.9.1 which is due shortly,
possibly today. The new test checks the Matplotlib version to know
whether uppercase backend module names are allowed or not.

IPython/core/magics/pylab.py

@@ -1,173 +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 _list_matplotlib_backends_and_gui_loops
 
             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)
+            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(
             "%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/tests/test_pylabtools.py

@@ -1,352 +1,375 b''
 """Tests for pylab tools module.
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 
 from binascii import a2b_base64
 from io import BytesIO
 
 import pytest
 
 matplotlib = pytest.importorskip("matplotlib")
 matplotlib.use('Agg')
 from matplotlib.figure import Figure
 
 from matplotlib import pyplot as plt
 from matplotlib_inline import backend_inline
 import numpy as np
 
 from IPython.core.getipython import get_ipython
 from IPython.core.interactiveshell import InteractiveShell
 from IPython.core.display import _PNG, _JPEG
 from .. import pylabtools as pt
 
 from IPython.testing import decorators as dec
 
 
 def test_figure_to_svg():
     # simple empty-figure test
     fig = plt.figure()
     assert pt.print_figure(fig, "svg") is None
 
     plt.close('all')
 
     # simple check for at least svg-looking output
     fig = plt.figure()
     ax = fig.add_subplot(1,1,1)
     ax.plot([1,2,3])
     plt.draw()
     svg = pt.print_figure(fig, "svg")[:100].lower()
     assert "doctype svg" in svg
 
 
 def _check_pil_jpeg_bytes():
     """Skip if PIL can't write JPEGs to BytesIO objects"""
     # PIL's JPEG plugin can't write to BytesIO objects
     # Pillow fixes this
     from PIL import Image
     buf = BytesIO()
     img = Image.new("RGB", (4,4))
     try:
         img.save(buf, 'jpeg')
     except Exception as e:
         ename = e.__class__.__name__
         raise pytest.skip("PIL can't write JPEG to BytesIO: %s: %s" % (ename, e)) from e
 
 @dec.skip_without("PIL.Image")
 def test_figure_to_jpeg():
     _check_pil_jpeg_bytes()
     # simple check for at least jpeg-looking output
     fig = plt.figure()
     ax = fig.add_subplot(1,1,1)
     ax.plot([1,2,3])
     plt.draw()
     jpeg = pt.print_figure(fig, 'jpeg', pil_kwargs={'optimize': 50})[:100].lower()
     assert jpeg.startswith(_JPEG)
 
 def test_retina_figure():
     # simple empty-figure test
     fig = plt.figure()
     assert pt.retina_figure(fig) == None
     plt.close('all')
 
     fig = plt.figure()
     ax = fig.add_subplot(1,1,1)
     ax.plot([1,2,3])
     plt.draw()
     png, md = pt.retina_figure(fig)
     assert png.startswith(_PNG)
     assert "width" in md
     assert "height" in md
 
 
 _fmt_mime_map = {
     'png': 'image/png',
     'jpeg': 'image/jpeg',
     'pdf': 'application/pdf',
     'retina': 'image/png',
     'svg': 'image/svg+xml',
 }
 
 def test_select_figure_formats_str():
     ip = get_ipython()
     for fmt, active_mime in _fmt_mime_map.items():
         pt.select_figure_formats(ip, fmt)
         for mime, f in ip.display_formatter.formatters.items():
             if mime == active_mime:
                 assert Figure in f
             else:
                 assert Figure not in f
 
 def test_select_figure_formats_kwargs():
     ip = get_ipython()
     kwargs = dict(bbox_inches="tight")
     pt.select_figure_formats(ip, "png", **kwargs)
     formatter = ip.display_formatter.formatters["image/png"]
     f = formatter.lookup_by_type(Figure)
     cell = f.keywords
     expected = kwargs
     expected["base64"] = True
     expected["fmt"] = "png"
     assert cell == expected
 
     # check that the formatter doesn't raise
     fig = plt.figure()
     ax = fig.add_subplot(1,1,1)
     ax.plot([1,2,3])
     plt.draw()
     formatter.enabled = True
     png = formatter(fig)
     assert isinstance(png, str)
     png_bytes = a2b_base64(png)
     assert png_bytes.startswith(_PNG)
 
 def test_select_figure_formats_set():
     ip = get_ipython()
     for fmts in [
         {'png', 'svg'},
         ['png'],
         ('jpeg', 'pdf', 'retina'),
         {'svg'},
     ]:
         active_mimes = {_fmt_mime_map[fmt] for fmt in fmts}
         pt.select_figure_formats(ip, fmts)
         for mime, f in ip.display_formatter.formatters.items():
             if mime in active_mimes:
                 assert Figure in f
             else:
                 assert Figure not in f
 
 def test_select_figure_formats_bad():
     ip = get_ipython()
     with pytest.raises(ValueError):
         pt.select_figure_formats(ip, 'foo')
     with pytest.raises(ValueError):
         pt.select_figure_formats(ip, {'png', 'foo'})
     with pytest.raises(ValueError):
         pt.select_figure_formats(ip, ['retina', 'pdf', 'bar', 'bad'])
 
 def test_import_pylab():
     ns = {}
     pt.import_pylab(ns, import_all=False)
     assert "plt" in ns
     assert ns["np"] == np
 
 
 class TestPylabSwitch(object):
     class Shell(InteractiveShell):
         def init_history(self):
             """Sets up the command history, and starts regular autosaves."""
             self.config.HistoryManager.hist_file = ":memory:"
             super().init_history()
 
         def enable_gui(self, gui):
             pass
 
     def setup_method(self):
         import matplotlib
         def act_mpl(backend):
             matplotlib.rcParams['backend'] = backend
 
         # Save rcParams since they get modified
         self._saved_rcParams = matplotlib.rcParams
         self._saved_rcParamsOrig = matplotlib.rcParamsOrig
         matplotlib.rcParams = dict(backend="QtAgg")
         matplotlib.rcParamsOrig = dict(backend="QtAgg")
 
         # Mock out functions
         self._save_am = pt.activate_matplotlib
         pt.activate_matplotlib = act_mpl
         self._save_ip = pt.import_pylab
         pt.import_pylab = lambda *a,**kw:None
         self._save_cis = backend_inline.configure_inline_support
         backend_inline.configure_inline_support = lambda *a, **kw: None
 
     def teardown_method(self):
         pt.activate_matplotlib = self._save_am
         pt.import_pylab = self._save_ip
         backend_inline.configure_inline_support = self._save_cis
         import matplotlib
         matplotlib.rcParams = self._saved_rcParams
         matplotlib.rcParamsOrig = self._saved_rcParamsOrig
 
     def test_qt(self):
         s = self.Shell()
         gui, backend = s.enable_matplotlib(None)
         assert gui == "qt"
         assert s.pylab_gui_select == "qt"
 
         gui, backend = s.enable_matplotlib("inline")
         assert gui is None
         assert s.pylab_gui_select == "qt"
 
         gui, backend = s.enable_matplotlib("qt")
         assert gui == "qt"
         assert s.pylab_gui_select == "qt"
 
         gui, backend = s.enable_matplotlib("inline")
         assert gui is None
         assert s.pylab_gui_select == "qt"
 
         gui, backend = s.enable_matplotlib()
         assert gui == "qt"
         assert s.pylab_gui_select == "qt"
 
     def test_inline(self):
         s = self.Shell()
         gui, backend = s.enable_matplotlib("inline")
         assert gui is None
         assert s.pylab_gui_select == None
 
         gui, backend = s.enable_matplotlib("inline")
         assert gui is None
         assert s.pylab_gui_select == None
 
         gui, backend = s.enable_matplotlib("qt")
         assert gui == "qt"
         assert s.pylab_gui_select == "qt"
 
     def test_inline_twice(self):
         "Using '%matplotlib inline' twice should not reset formatters"
 
         ip = self.Shell()
         gui, backend = ip.enable_matplotlib("inline")
         assert gui is None
 
         fmts =  {'png'}
         active_mimes = {_fmt_mime_map[fmt] for fmt in fmts}
         pt.select_figure_formats(ip, fmts)
 
         gui, backend = ip.enable_matplotlib("inline")
         assert gui is None
 
         for mime, f in ip.display_formatter.formatters.items():
             if mime in active_mimes:
                 assert Figure in f
             else:
                 assert Figure not in f
 
     def test_qt_gtk(self):
         s = self.Shell()
         gui, backend = s.enable_matplotlib("qt")
         assert gui == "qt"
         assert s.pylab_gui_select == "qt"
 
         gui, backend = s.enable_matplotlib("gtk3")
         assert gui == "qt"
         assert s.pylab_gui_select == "qt"
 
+    @dec.skipif(not pt._matplotlib_manages_backends())
+    def test_backend_module_name_case_sensitive(self):
+        # Matplotlib backend names are case insensitive unless explicitly specified using
+        # "module://some_module.some_name" syntax which are case sensitive for mpl >= 3.9.1
+        all_lowercase = "module://matplotlib_inline.backend_inline"
+        some_uppercase = "module://matplotlib_inline.Backend_inline"
+        mpl3_9_1 = matplotlib.__version_info__ >= (3, 9, 1)
+
+        s = self.Shell()
+        s.enable_matplotlib(all_lowercase)
+        if mpl3_9_1:
+            with pytest.raises(RuntimeError):
+                s.enable_matplotlib(some_uppercase)
+        else:
+            s.enable_matplotlib(some_uppercase)
+
+        s.run_line_magic("matplotlib", all_lowercase)
+        if mpl3_9_1:
+            with pytest.raises(RuntimeError):
+                s.run_line_magic("matplotlib", some_uppercase)
+        else:
+            s.run_line_magic("matplotlib", some_uppercase)
+
 
 def test_no_gui_backends():
     for k in ['agg', 'svg', 'pdf', 'ps']:
         assert k not in pt.backend2gui
 
 
 def test_figure_no_canvas():
     fig = Figure()
     fig.canvas = None
     pt.print_figure(fig)
 
 
 @pytest.mark.parametrize(
     "name, expected_gui, expected_backend",
     [
         # name is gui
         ("gtk3", "gtk3", "gtk3agg"),
         ("gtk4", "gtk4", "gtk4agg"),
         ("headless", None, "agg"),
         ("osx", "osx", "macosx"),
         ("qt", "qt", "qtagg"),
         ("qt5", "qt5", "qt5agg"),
         ("qt6", "qt6", "qtagg"),
         ("tk", "tk", "tkagg"),
         ("wx", "wx", "wxagg"),
         # name is backend
         ("agg", None, "agg"),
         ("cairo", None, "cairo"),
         ("pdf", None, "pdf"),
         ("ps", None, "ps"),
         ("svg", None, "svg"),
         ("template", None, "template"),
         ("gtk3agg", "gtk3", "gtk3agg"),
         ("gtk3cairo", "gtk3", "gtk3cairo"),
         ("gtk4agg", "gtk4", "gtk4agg"),
         ("gtk4cairo", "gtk4", "gtk4cairo"),
         ("macosx", "osx", "macosx"),
         ("nbagg", "nbagg", "nbagg"),
         ("notebook", "nbagg", "notebook"),
         ("qtagg", "qt", "qtagg"),
         ("qtcairo", "qt", "qtcairo"),
         ("qt5agg", "qt5", "qt5agg"),
         ("qt5cairo", "qt5", "qt5cairo"),
         ("tkagg", "tk", "tkagg"),
         ("tkcairo", "tk", "tkcairo"),
         ("webagg", "webagg", "webagg"),
         ("wxagg", "wx", "wxagg"),
         ("wxcairo", "wx", "wxcairo"),
     ],
 )
 def test_backend_builtin(name, expected_gui, expected_backend):
     # Test correct identification of Matplotlib built-in backends without importing and using them,
     # otherwise we would need to ensure all the complex dependencies such as windowing toolkits are
     # installed.
 
     mpl_manages_backends = pt._matplotlib_manages_backends()
     if not mpl_manages_backends:
         # Backends not supported before _matplotlib_manages_backends or supported
         # but with different expected_gui or expected_backend.
         if (
             name.endswith("agg")
             or name.endswith("cairo")
             or name in ("headless", "macosx", "pdf", "ps", "svg", "template")
         ):
             pytest.skip()
         elif name == "qt6":
             expected_backend = "qtagg"
         elif name == "notebook":
             expected_backend, expected_gui = expected_gui, expected_backend
 
     gui, backend = pt.find_gui_and_backend(name)
     if not mpl_manages_backends:
         gui = gui.lower() if gui else None
         backend = backend.lower() if backend else None
     assert gui == expected_gui
     assert backend == expected_backend
 
 
 def test_backend_entry_point():
     gui, backend = pt.find_gui_and_backend("inline")
     assert gui is None
     expected_backend = (
         "inline"
         if pt._matplotlib_manages_backends()
         else "module://matplotlib_inline.backend_inline"
     )
     assert backend == expected_backend
 
 
 def test_backend_unknown():
     with pytest.raises(RuntimeError if pt._matplotlib_manages_backends() else KeyError):
         pt.find_gui_and_backend("name-does-not-exist")