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MNT: handle generic descriptors in _setattr_cm #17561

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MNT: handle generic descriptors in _setattr_cm #17561

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19 changes: 14 additions & 5 deletions lib/matplotlib/cbook/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
import contextlib
import functools
import gzip
import inspect
import itertools
import math
import operator
Expand Down Expand Up @@ -1961,6 +1962,10 @@ def _array_patch_perimeters(x, rstride, cstride):
def _setattr_cm(obj, **kwargs):
"""
Temporarily set some attributes; restore original state at context exit.

.. warning ::

This is not threadsafe.
"""
sentinel = object()
origs = {}
Expand All @@ -1978,14 +1983,18 @@ def _setattr_cm(obj, **kwargs):
# we want to set the original value back.
if isinstance(cls_orig, property):
origs[attr] = orig

# detect when we have Python Descriptors that supports
# setting so we will need to restore it
#
# https://docs.python.org/3/howto/descriptor.html
if hasattr(inspect.getattr_static(type(obj), attr), '__set__'):
origs[attr] = orig

# otherwise this is _something_ we are going to shadow at
# the instance dict level from higher up in the MRO. We
# are going to assume we can delattr(obj, attr) to clean
# up after ourselves. It is possible that this code will
# fail if used with a non-property custom descriptor which
# implements __set__ (and __delete__ does not act like a
# stack). However, this is an internal tool and we do not
# currently have any custom descriptors.
# up after ourselves.
else:
origs[attr] = sentinel

Expand Down