Description
Bug report
If you apply this diff to typing.py
, all tests continue to pass:
diff --git a/Lib/typing.py b/Lib/typing.py
index 1dd9398344..98e19644a2 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1931,6 +1931,7 @@ def _proto_hook(other):
if (isinstance(annotations, collections.abc.Mapping) and
attr in annotations and
issubclass(other, Generic) and getattr(other, '_is_protocol', False)):
+ 1/0
break
The break
on line 1934 here is unreachable; thus, this whole block of code is pointless:
Lines 1929 to 1934 in 3af2dc7
I think we can say for sure that the break
here is unreachable. This is the __subclasshook__
method that is monkey-patched onto all subclasses of typing.Protocol
that do not define their own __subclasshook__
methods. This block of code in the __subclasshook__
method is inspecting the __annotations__
dictionary of other
to see if it can find any protocol members in that dictionary. But we know that there can't be any protocol members in the __annotations__
dictionary, because if there were, that would make other
a protocol with at least one non-callable member. If it's a protocol that has at least one non-callable member, the __subclasshook__
method is never called at all during isinstance()
or issubclass()
checks, because we raise TypeError
in _ProtocolMeta.__subclasscheck__
, short-circuiting the call to abc.ABCMeta.__subclasscheck__
that would call Protocol.__subclasshook__
:
Lines 1828 to 1831 in 3af2dc7
I believe that this block of code can therefore be safely deleted.