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gh-103193: cache calls to inspect._shadowed_dict in `inspect.getatt…
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…r_static` (#104267)

Co-authored-by: Carl Meyer <carl@oddbird.net>
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AlexWaygood and carljm authored May 7, 2023
1 parent 60f5884 commit 1b19bd1
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Showing 3 changed files with 32 additions and 5 deletions.
7 changes: 4 additions & 3 deletions Doc/whatsnew/3.12.rst
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Expand Up @@ -342,8 +342,9 @@ inspect
(Contributed by Thomas Krennwallner in :issue:`35759`.)

* The performance of :func:`inspect.getattr_static` has been considerably
improved. Most calls to the function should be around 2x faster than they
were in Python 3.11. (Contributed by Alex Waygood in :gh:`103193`.)
improved. Most calls to the function should be at least 2x faster than they
were in Python 3.11, and some may be 6x faster or more. (Contributed by Alex
Waygood in :gh:`103193`.)

pathlib
-------
Expand Down Expand Up @@ -597,7 +598,7 @@ typing
:func:`runtime-checkable protocols <typing.runtime_checkable>` has changed
significantly. Most ``isinstance()`` checks against protocols with only a few
members should be at least 2x faster than in 3.11, and some may be 20x
faster or more. However, ``isinstance()`` checks against protocols with seven
faster or more. However, ``isinstance()`` checks against protocols with fourteen
or more members may be slower than in Python 3.11. (Contributed by Alex
Waygood in :gh:`74690` and :gh:`103193`.)

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8 changes: 6 additions & 2 deletions Lib/inspect.py
Original file line number Diff line number Diff line change
Expand Up @@ -1794,8 +1794,9 @@ def _check_class(klass, attr):
return entry.__dict__[attr]
return _sentinel

def _shadowed_dict(klass):
for entry in _static_getmro(klass):
@functools.lru_cache()
def _shadowed_dict_from_mro_tuple(mro):
for entry in mro:
dunder_dict = _get_dunder_dict_of_class(entry)
if '__dict__' in dunder_dict:
class_dict = dunder_dict['__dict__']
Expand All @@ -1805,6 +1806,9 @@ def _shadowed_dict(klass):
return class_dict
return _sentinel

def _shadowed_dict(klass):
return _shadowed_dict_from_mro_tuple(_static_getmro(klass))

def getattr_static(obj, attr, default=_sentinel):
"""Retrieve attributes without triggering dynamic lookup via the
descriptor protocol, __getattr__ or __getattribute__.
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22 changes: 22 additions & 0 deletions Lib/test/test_inspect.py
Original file line number Diff line number Diff line change
Expand Up @@ -2111,6 +2111,28 @@ def __dict__(self):
self.assertEqual(inspect.getattr_static(foo, 'a'), 3)
self.assertFalse(test.called)

def test_mutated_mro(self):
test = self
test.called = False

class Foo(dict):
a = 3
@property
def __dict__(self):
test.called = True
return {}

class Bar(dict):
a = 4

class Baz(Bar): pass

baz = Baz()
self.assertEqual(inspect.getattr_static(baz, 'a'), 4)
Baz.__bases__ = (Foo,)
self.assertEqual(inspect.getattr_static(baz, 'a'), 3)
self.assertFalse(test.called)

def test_custom_object_dict(self):
test = self
test.called = False
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