8000 gh-74690: typing: Call `_get_protocol_attrs` and `_callable_members_only` at protocol class creation time, not during `isinstance()` checks by AlexWaygood · Pull Request #103160 · python/cpython · GitHub
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gh-74690: typing: Call _get_protocol_attrs and _callable_members_only at protocol class creation time, not during isinstance() checks #103160

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Merged
merged 9 commits into from
Apr 5, 2023
Merged

gh-74690: typing: Call _get_protocol_attrs and _callable_members_only at protocol class creation time, not during isinstance() checks #103160

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f15c64a
gh-74690: typing: Cache results of `_get_protocol_attrs` and `_callab…
AlexWaygood Mar 31, 2023
f3ec3db
Simplify and inline
AlexWaygood Apr 1, 2023
8e3c6f7
Use a metaclass instance method, not a classmethod on the class
AlexWaygood Apr 1, 2023
a34f700
Move to class-creation time
AlexWaygood Apr 1, 2023
4d05074
Use `__init__`, not `__new__`
AlexWaygood Apr 1, 2023
d3f9ebe
Add missing `super().__init__()` call, to be safe
AlexWaygood Apr 1, 2023
e8a6304
Merge branch 'main' into protocol-attrs-cache-1
AlexWaygood Apr 2, 2023
4816afa
Merge branch 'main' into protocol-attrs-cache-1
AlexWaygood Apr 5, 2023
08af615
Update Lib/typing.py
AlexWaygood Apr 5, 2023
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31 changes: 14 additions & 17 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1905,7 +1905,8 @@ class _TypingEllipsis:

_TYPING_INTERNALS = frozenset({
'__parameters__', '__orig_bases__', '__orig_class__',
'_is_protocol', '_is_runtime_protocol'
'_is_protocol', '_is_runtime_protocol', '__protocol_attrs__',
'__callable_proto_members_only__',
})

_SPECIAL_NAMES = frozenset({
Expand Down Expand Up @@ -1935,11 +1936,6 @@ def _get_protocol_attrs(cls):
return attrs


def _is_callable_members_only(cls, protocol_attrs):
# PEP 544 prohibits using issubclass() with protocols that have non-method members.
return all(callable(getattr(cls, attr, None)) for attr in protocol_attrs)


def _no_init_or_replace_init(self, *args, **kwargs):
cls = type(self)

Expand Down Expand Up @@ -2001,6 +1997,14 @@ def _allow_reckless_class_checks(depth=3):
class _ProtocolMeta(ABCMeta):
# This metaclass is really unfortunate and exists only because of
# the lack of __instancehook__.
def __init__(cls, *args, **kwargs):
cls.__protocol_attrs__ = _get_protocol_attrs(cls)
# PEP 544 prohibits using issubclass()
# with protocols that have non-method members.
cls.__callable_proto_members_only__ = all(
callable(getattr(cls, attr, None)) for attr in cls.__protocol_attrs__
)
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@AlexWaygood AlexWaygood Apr 1, 2023 •
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The only reason I'm adding this method here rather than doing this work in Protocol.__init_subclass__ is that it seems slightly more backwards-compatible. With this PR, _ProtcolMeta.__instancecheck__ assumes that all classes with _ProtocolMeta as their metaclass will have a __protocol_attrs__ attribute. Since _ProtocolMeta is an undocumented implementation detail, it should only be Protocol and Protocol subclasses using _ProtocolMeta as their metaclass, and if we could count on that, then it would be safe to do this work in Protocol.__init_subclass__. But it's possible users might have been reaching into the internals of typing.py and creating other classes that use _ProtocolMeta as their metaclass, and I don't want to risk breaking their code unnecessarily.

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Confirmed that there's at least a few uses of _ProtocolMeta out in the wild:

https://github.com/antonagestam/phantom-types/blob/68ee857af4452a90a48669a8dbc7d1d7110b31d0/src/phantom/sized.py#L71-L82

https://github.com/protolambda/remerkleable/blob/91ed092d08ef0ba5ab076f0a34b0b371623db728/remerkleable/core.py#L18-L22

https://github.com/InterStella0/stella_bot/blob/bf5f5632bcd88670df90be67b888c282c6e83d99/utils/useful.py#L337-L343


def __instancecheck__(cls, instance):
# We need this method for situations where attributes are
# assigned in __init__.
Expand All @@ -2016,20 +2020,15 @@ def __instancecheck__(cls, instance):
if not is_protocol_cls and issubclass(instance.__class__, cls):
return True

protocol_attrs = _get_protocol_attrs(cls)

if (
_is_callable_members_only(cls, protocol_attrs)
and issubclass(instance.__class__, cls)
):
if cls.__callable_proto_members_only__ and issubclass(instance.__class__, cls):
return True

if is_protocol_cls:
if all(hasattr(instance, attr) and
# All *methods* can be blocked by setting them to None.
(not callable(getattr(cls, attr, None)) or
getattr(instance, attr) is not None)
for attr in protocol_attrs):
for attr in cls.__protocol_attrs__):
return True
return super().__instancecheck__(instance)

Expand Down Expand Up @@ -2087,9 +2086,7 @@ def _proto_hook(other):
raise TypeError("Instance and class checks can only be used with"
" @runtime_checkable protocols")

protocol_attrs = _get_protocol_attrs(cls)

if not _is_callable_members_only(cls, protocol_attrs):
if not cls.__callable_proto_members_only__ :
if _allow_reckless_class_checks():
return NotImplemented
raise TypeError("Protocols with non-method members"
Expand All @@ -2099,7 +2096,7 @@ def _proto_hook(other):
raise TypeError('issubclass() arg 1 must be a class')

# Second, perform the actual structural compatibility check.
for attr in protocol_attrs:
for attr in cls.__protocol_attrs__:
for base in other.__mro__:
# Check if the members appears in the class dictionary...
if attr in base.__dict__:
Expand Down
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