Inconsistency with a variable defined inside an exclusive if.

[marmistrz]

mypy 0.521

Let's take this snippet. This one is perfectly fine and mypy doesn't complain

x = 7
if x == 7:
    v = 42
else:
    pass

Now, let's add another branch:

x = 7
if x == 7:
    v = 42
elif x == 8:
    v = "42"
else:
    pass

This triggers an error:

/tmp/test.py:5: error: Incompatible types in assignment (expression has type "str", variable has type "int")

It shouldn't, since the variable is not used outside the if...elif...else

[Daenyth]

Python doesn't have block level scoping though, so v can be referenced outside the if/elif block once it's completed

[refi64]

I think the inconsistency here is that v will be undefined if the condition is false?

[ilevkivskyi]

Thank you for reporting! I dont think this is a new bug/feature request. We already have a proposal to infer Union across an if ... else ... (see #2611) so I am closing this issue.