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Deprecate backend_qt.qApp. #22503

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merged 2 commits into from
Mar 22, 2022
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Deprecate backend_qt.qApp. #22503

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32935fd
Deprecate backend_qt.qApp.
anntzer Feb 19, 2022
88377a3
TST: add test of qApp access warning
tacaswell Mar 22, 2022
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3 changes: 3 additions & 0 deletions doc/api/next_api_changes/deprecations/22503-AL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
``backend_qt.qApp``
~~~~~~~~~~~~~~~~~~~
... is deprecated. Use ``QtWidgets.QApplication.instance()`` instead.
122 changes: 63 additions & 59 deletions lib/matplotlib/backends/backend_qt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -92,70 +92,73 @@
}


# make place holder
qApp = None
@_api.caching_module_getattr
class __getattr__:
qApp = _api.deprecated(
"3.6", alternative="QtWidgets.QApplication.instance()")(
property(lambda self: QtWidgets.QApplication.instance()))


# lru_cache keeps a reference to the QApplication instance, keeping it from
# being GC'd.
@functools.lru_cache(1)
def _create_qApp():
"""
Only one qApp can exist at a time, so check before creating one.
"""
global qApp

if qApp is None:
app = QtWidgets.QApplication.instance()
if app is None:
# display_is_valid returns False only if on Linux and neither X11
# nor Wayland display can be opened.
if not mpl._c_internal_utils.display_is_valid():
raise RuntimeError('Invalid DISPLAY variable')
try:
QtWidgets.QApplication.setAttribute(
QtCore.Qt.AA_EnableHighDpiScaling)
except AttributeError: # Only for Qt>=5.6, <6.
pass

# Check to make sure a QApplication from a different major version
# of Qt is not instantiated in the process
if QT_API in {'PyQt6', 'PySide6'}:
other_bindings = ('PyQt5', 'PySide2')
elif QT_API in {'PyQt5', 'PySide2'}:
other_bindings = ('PyQt6', 'PySide6')
else:
raise RuntimeError("Should never be here")

for binding in other_bindings:
mod = sys.modules.get(f'{binding}.QtWidgets')
if mod is not None and mod.QApplication.instance() is not None:
other_core = sys.modules.get(f'{binding}.QtCore')
_api.warn_external(
f'Matplotlib is using {QT_API} which wraps '
f'{QtCore.qVersion()} however an instantiated '
f'QApplication from {binding} which wraps '
f'{other_core.qVersion()} exists. Mixing Qt major '
'versions may not work as expected.'
)
break
try:
QtWidgets.QApplication.setHighDpiScaleFactorRoundingPolicy(
QtCore.Qt.HighDpiScaleFactorRoundingPolicy.PassThrough)
except AttributeError: # Only for Qt>=5.14.
pass
qApp = QtWidgets.QApplication(["matplotlib"])
if sys.platform == "darwin":
image = str(cbook._get_data_path('images/matplotlib.svg'))
icon = QtGui.QIcon(image)
qApp.setWindowIcon(icon)
qApp.lastWindowClosed.connect(qApp.quit)
cbook._setup_new_guiapp()
app = QtWidgets.QApplication.instance()

# Create a new QApplication and configure if if non exists yet, as only one
# QApplication can exist at a time.
if app is None:
# display_is_valid returns False only if on Linux and neither X11
# nor Wayland display can be opened.
if not mpl._c_internal_utils.display_is_valid():
raise RuntimeError('Invalid DISPLAY variable')

# Check to make sure a QApplication from a different major version
# of Qt is not instantiated in the process
if QT_API in {'PyQt6', 'PySide6'}:
other_bindings = ('PyQt5', 'PySide2')
elif QT_API in {'PyQt5', 'PySide2'}:
other_bindings = ('PyQt6', 'PySide6')
else:
qApp = app
raise RuntimeError("Should never be here")

for binding in other_bindings:
mod = sys.modules.get(f'{binding}.QtWidgets')
if mod is not None and mod.QApplication.instance() is not None:
other_core = sys.modules.get(f'{binding}.QtCore')
_api.warn_external(
f'Matplotlib is using {QT_API} which wraps '
f'{QtCore.qVersion()} however an instantiated '
f'QApplication from {binding} which wraps '
f'{other_core.qVersion()} exists. Mixing Qt major '
'versions may not work as expected.'
)
break
try:
QtWidgets.QApplication.setAttribute(
QtCore.Qt.AA_EnableHighDpiScaling)
except AttributeError: # Only for Qt>=5.6, <6.
pass
try:
QtWidgets.QApplication.setHighDpiScaleFactorRoundingPolicy(
QtCore.Qt.HighDpiScaleFactorRoundingPolicy.PassThrough)
except AttributeError: # Only for Qt>=5.14.
pass
app = QtWidgets.QApplication(["matplotlib"])
if sys.platform == "darwin":
image = str(cbook._get_data_path('images/matplotlib.svg'))
icon = QtGui.QIcon(image)
app.setWindowIcon(icon)
app.lastWindowClosed.connect(app.quit)
cbook._setup_new_guiapp()

try:
qApp.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps) # Only for Qt<6.
app.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps) # Only for Qt<6.
except AttributeError:
pass

return app


def _allow_super_init(__init__):
"""
Expand Down Expand Up @@ -419,7 +422,7 @@ def _get_key(self, event):

def flush_events(self):
# docstring inherited
qApp.processEvents()
QtWidgets.QApplication.instance().processEvents()

def start_event_loop(self, timeout=0):
# docstring inherited
Expand Down Expand Up @@ -1022,7 +1025,7 @@ def trigger(self, *args):
class ToolCopyToClipboardQT(backend_tools.ToolCopyToClipboardBase):
def trigger(self, *args, **kwargs):
pixmap = self.canvas.grab()
qApp.clipboard().setPixmap(pixmap)
QtWidgets.QApplication.instance().clipboard().setPixmap(pixmap)


FigureManagerQT._toolbar2_class = NavigationToolbar2QT
Expand All @@ -1036,5 +1039,6 @@ class _BackendQT(_Backend):

@staticmethod
def mainloop():
with _maybe_allow_interrupt(qApp):
qt_compat._exec(qApp)
qapp = QtWidgets.QApplication.instance()
with _maybe_allow_interrupt(qapp):
qt_compat._exec(qapp)
29 changes: 25 additions & 4 deletions lib/matplotlib/tests/test_backends_interactive.py
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Original file line number Diff line number Diff line change
Expand Up @@ -267,7 +267,9 @@ def _implqt5agg():
assert 'PyQt5' in sys.modules or 'pyside2' in sys.modules

import matplotlib.backends.backend_qt5
matplotlib.backends.backend_qt5.qApp
with pytest.warns(DeprecationWarning,
match="QtWidgets.QApplication.instance"):
matplotlib.backends.backend_qt5.qApp


def _implcairo():
Expand All @@ -279,7 +281,9 @@ def _implcairo():
assert 'PyQt5' in sys.modules or 'pyside2' in sys.modules

import matplotlib.backends.backend_qt5
matplotlib.backends.backend_qt5.qApp
with pytest.warns(DeprecationWarning,
match="QtWidgets.QApplication.instance"):
matplotlib.backends.backend_qt5.qApp


def _implcore():
Expand All @@ -289,7 +293,10 @@ def _implcore():
assert 'PyQt6' not in sys.modules
assert 'pyside6' not in sys.modules
assert 'PyQt5' in sys.modules or 'pyside2' in sys.modules
matplotlib.backends.backend_qt5.qApp

with pytest.warns(DeprecationWarning,
match="QtWidgets.QApplication.instance"):
matplotlib.backends.backend_qt5.qApp


def test_qt5backends_uses_qt5():
Expand Down Expand Up @@ -410,11 +417,25 @@ def _lazy_headless():


@pytest.mark.skipif(sys.platform != "linux", reason="this a linux-only test")
@pytest.mark.backend('QtAgg', skip_on_importerror=True)
@pytest.mark.backend('Qt5Agg', skip_on_importerror=True)
def test_lazy_linux_headless():
proc = _run_helper(_lazy_headless, timeout=_test_timeout, MPLBACKEND="")


def _qApp_warn_impl():
import matplotlib.backends.backend_qt
import pytest

with pytest.warns(
DeprecationWarning, match="QtWidgets.QApplication.instance"):
matplotlib.backends.backend_qt.qApp


@pytest.mark.backend('QtAgg', skip_on_importerror=True)
def test_qApp_warn():
_run_helper(_qApp_warn_impl, timeout=_test_timeout)


def _test_number_of_draws_script():
import matplotlib.pyplot as plt

Expand Down