From 42b48ceeb57da28db347eb11e7a3e61e78526485 Mon Sep 17 00:00:00 2001 From: Alex Waygood Date: Thu, 18 May 2023 00:43:12 +0100 Subject: [PATCH] gh-104555: Runtime-checkable protocols: Don't let previous calls to `isinstance()` influence whether `issubclass()` raises an exception (#104559) Co-authored-by: Carl Meyer --- Lib/test/test_typing.py | 76 +++++++++++++++++++ Lib/typing.py | 20 +++-- ...-05-17-16-58-23.gh-issue-104555.5rb5oM.rst | 7 ++ 3 files changed, 96 insertions(+), 7 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2023-05-17-16-58-23.gh-issue-104555.5rb5oM.rst diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py index 045f2a3b4dfe18f..bf038bf143a6c80 100644 --- a/Lib/test/test_typing.py +++ b/Lib/test/test_typing.py @@ -2695,6 +2695,82 @@ class D(PNonCall): ... with self.assertRaises(TypeError): issubclass(D, PNonCall) + def test_no_weird_caching_with_issubclass_after_isinstance(self): + @runtime_checkable + class Spam(Protocol): + x: int + + class Eggs: + def __init__(self) -> None: + self.x = 42 + + self.assertIsInstance(Eggs(), Spam) + + # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta, + # TypeError wouldn't be raised here, + # as the cached result of the isinstance() check immediately above + # would mean the issubclass() call would short-circuit + # before we got to the "raise TypeError" line + with self.assertRaises(TypeError): + issubclass(Eggs, Spam) + + def test_no_weird_caching_with_issubclass_after_isinstance_2(self): + @runtime_checkable + class Spam(Protocol): + x: int + + class Eggs: ... + + self.assertNotIsInstance(Eggs(), Spam) + + # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta, + # TypeError wouldn't be raised here, + # as the cached result of the isinstance() check immediately above + # would mean the issubclass() call would short-circuit + # before we got to the "raise TypeError" line + with self.assertRaises(TypeError): + issubclass(Eggs, Spam) + + def test_no_weird_caching_with_issubclass_after_isinstance_3(self): + @runtime_checkable + class Spam(Protocol): + x: int + + class Eggs: + def __getattr__(self, attr): + if attr == "x": + return 42 + raise AttributeError(attr) + + self.assertNotIsInstance(Eggs(), Spam) + + # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta, + # TypeError wouldn't be raised here, + # as the cached result of the isinstance() check immediately above + # would mean the issubclass() call would short-circuit + # before we got to the "raise TypeError" line + with self.assertRaises(TypeError): + issubclass(Eggs, Spam) + + def test_no_weird_caching_with_issubclass_after_isinstance_pep695(self): + @runtime_checkable + class Spam[T](Protocol): + x: T + + class Eggs[T]: + def __init__(self, x: T) -> None: + self.x = x + + self.assertIsInstance(Eggs(42), Spam) + + # gh-104555: If we didn't override ABCMeta.__subclasscheck__ in _ProtocolMeta, + # TypeError wouldn't be raised here, + # as the cached result of the isinstance() check immediately above + # would mean the issubclass() call would short-circuit + # before we got to the "raise TypeError" line + with self.assertRaises(TypeError): + issubclass(Eggs, Spam) + def test_protocols_isinstance(self): T = TypeVar('T') diff --git a/Lib/typing.py b/Lib/typing.py index 82107300734a7b4..91b5fe5b87e6691 100644 --- a/Lib/typing.py +++ b/Lib/typing.py @@ -1775,8 +1775,8 @@ def _pickle_pskwargs(pskwargs): class _ProtocolMeta(ABCMeta): - # This metaclass is really unfortunate and exists only because of - # the lack of __instancehook__. + # This metaclass is somewhat unfortunate, + # but is necessary for several reasons... def __init__(cls, *args, **kwargs): super().__init__(*args, **kwargs) cls.__protocol_attrs__ = _get_protocol_attrs(cls) @@ -1786,6 +1786,17 @@ def __init__(cls, *args, **kwargs): callable(getattr(cls, attr, None)) for attr in cls.__protocol_attrs__ ) + def __subclasscheck__(cls, other): + if ( + getattr(cls, '_is_protocol', False) + and not cls.__callable_proto_members_only__ + and not _allow_reckless_class_checks(depth=2) + ): + raise TypeError( + "Protocols with non-method members don't support issubclass()" + ) + return super().__subclasscheck__(other) + def __instancecheck__(cls, instance): # We need this method for situations where attributes are # assigned in __init__. @@ -1869,11 +1880,6 @@ def _proto_hook(other): raise TypeError("Instance and class checks can only be used with" " @runtime_checkable protocols") - if not cls.__callable_proto_members_only__ : - if _allow_reckless_class_checks(): - return NotImplemented - raise TypeError("Protocols with non-method members" - " don't support issubclass()") if not isinstance(other, type): # Same error message as for issubclass(1, int). raise TypeError('issubclass() arg 1 must be a class') diff --git a/Misc/NEWS.d/next/Library/2023-05-17-16-58-23.gh-issue-104555.5rb5oM.rst b/Misc/NEWS.d/next/Library/2023-05-17-16-58-23.gh-issue-104555.5rb5oM.rst new file mode 100644 index 000000000000000..2992346484c5fab --- /dev/null +++ b/Misc/NEWS.d/next/Library/2023-05-17-16-58-23.gh-issue-104555.5rb5oM.rst @@ -0,0 +1,7 @@ +Fix issue where an :func:`issubclass` check comparing a class ``X`` against a +:func:`runtime-checkable protocol ` ``Y`` with +non-callable members would not cause :exc:`TypeError` to be raised if an +:func:`isinstance` call had previously been made comparing an instance of ``X`` +to ``Y``. This issue was present in edge cases on Python 3.11, but became more +prominent in 3.12 due to some unrelated changes that were made to +runtime-checkable protocols. Patch by Alex Waygood.