Union as type of a Dict fails, when coming from a variable

[ltworf]

This possibly relates to this #6463

from typing import *

def f(arg: Sequence[Dict[Union[int,str], str]]) -> None:
    ...

def q(arg: Sequence[Union[int,str]]) -> None:
    ...

q([1,2,3,'a']) # This works
f([{'a':'a'}]) # This works

l =  [{'a':'a'}]
f(l) # This does not

It seems that assigning the same value to a variable or passing it directly gets typed differently for some reason.

[JelleZijlstra]

See https://mypy.readthedocs.io/en/stable/common_issues.html#invariance-vs-covariance.

[ltworf]

The type of the same thing is being inferred differently depending if it's assigned to a variable or passed as a parameter. That is what I'm reporting here.

[JelleZijlstra]

That's also expected behavior. If you assign it to a variable, the type of the variable is fixed at the definition site, but if you use a literal as an argument to a function mypy uses type context to infer a different type.