Summary
We currently emit a diagnostic when an invalid types.UnionType instance is used as the second argument to isinstance() or issubclass(). But we do not currently detect this if the types.UnionType instance is nested inside a tuple.
It's probably not high-priority to fix this because I'm not sure why you'd write code like this, but it's a known edge case that we don't handle currently, so it seemed worth opening an issue about.
from typing import Literal
def f(x):
if isinstance(x, str | Literal[42]): # diagnostic (good! this fails at runtime)
reveal_type(x)
if isinstance(x, (int, str | Literal[42])): # no diagnostic
reveal_type(x) # revealed: Unknown
if isinstance(x, (int, (str, (bytes, memoryview | Literal[42])))): # no diagnostic
reveal_type(x) # revealed: UnknownAt runtime:
Python 3.13.1 (main, Jan 3 2025, 12:04:03) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing import Literal
>>> if isinstance(42, (bytes, str | int)):
... print('got you')
...
got you
>>> if isinstance(42, (bytes, str | Literal[42])):
... print('got you')
...
Traceback (most recent call last):
File "<python-input-3>", line 1, in <module>
if isinstance(42, (bytes, str | Literal[42])):
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/typing.py", line 1786, in __instancecheck__
return self.__subclasscheck__(type(obj))
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/typing.py", line 1790, in __subclasscheck__
if issubclass(cls, arg):
~~~~~~~~~~^^^^^^^^^^
File "/Users/alexw/.pyenv/versions/3.13.1/lib/python3.13/typing.py", line 1378, in __subclasscheck__
raise TypeError("Subscripted generics cannot be used with"
" class and instance checks")
TypeError: Subscripted generics cannot be used with class and instance checksVersion
No response
Summary
We currently emit a diagnostic when an invalid
types.UnionTypeinstance is used as the second argument toisinstance()orissubclass(). But we do not currently detect this if thetypes.UnionTypeinstance is nested inside a tuple.It's probably not high-priority to fix this because I'm not sure why you'd write code like this, but it's a known edge case that we don't handle currently, so it seemed worth opening an issue about.
At runtime:
Version
No response