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Make guiEvent available only within the event handlers. #25559

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Merged
merged 1 commit into from
Mar 28, 2023
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Make guiEvent available only within the event handlers. #25559

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5 changes: 5 additions & 0 deletions doc/api/next_api_changes/deprecations/25559-AL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
Accessing ``event.guiEvent`` after event handlers return
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
... is deprecated: for some GUI toolkits, it is unsafe to do so. In the
future, ``event.guiEvent`` will be set to None once the event handlers return;
you may separately stash the object at your own risk.
19 changes: 17 additions & 2 deletions lib/matplotlib/backend_bases.py
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Expand Up @@ -1257,11 +1257,26 @@ class Event:
def __init__(self, name, canvas, guiEvent=None):
self.name = name
self.canvas = canvas
self.guiEvent = guiEvent
self._guiEvent = guiEvent
self._guiEvent_deleted = False

def _process(self):
"""Generate an event with name ``self.name`` on ``self.canvas``."""
"""Process this event on ``self.canvas``, then unset ``guiEvent``."""
self.canvas.callbacks.process(self.name, self)
self._guiEvent_deleted = True

@property
def guiEvent(self):
# After deprecation elapses: remove _guiEvent_deleted; make guiEvent a plain
# attribute set to None by _process.
if self._guiEvent_deleted:
_api.warn_deprecated(
"3.8", message="Accessing guiEvent outside of the original GUI event "
"handler is unsafe and deprecated since %(since)s; in the future, the "
"attribute will be set to None after quitting the event handler. You "
"may separately record the value of the guiEvent attribute at your own "
"risk.")
return self._guiEvent


class DrawEvent(Event):
Expand Down