type of Union containing Any is incorrectly inferred after an isinstance check

[sharmaeklavya2]

union_any.py:

from typing import Any, Union

def func(v):
 # type: (Union[int, Any]) -> str
 if isinstance(v, int):
 s = hex(v)
 else:
 s = str(v).lower()
 return "key:" + s

mypy union_any.py:

union_any.py: note: In function "func":
union_any.py:8: error: No overload variant of "str" matches argument types [Union[<ERROR>, void]]

mypy --py2 union_any.py:

union_any.py: note: In function "func":
union_any.py:8: error: Argument 1 to "str" has incompatible type "Union[object, None]"; expected "object"

I discovered this when I used a class which was defined in some library which did not have stubs and I was using --silent-imports.

[ddfisher]

In addition to being a Union[Any, ...] -> Any problem, I think this is at least vaguely related to #1691.

[sharmaeklavya2]

Another case where I found this error is when 2 classes inherit from Any:

file1.py:

from typing import Any, Union

class B(Any): name = 'Bob'
class C(Any): name = 'Charlie'

def func(x):
 # type: (Union[B, C]) -> None
 reveal_type(x)
 if isinstance(x, B):
 reveal_type(x)
 print(x.name)
 else:
 reveal_type(x)
 print(x.name)

gives this output:

file1.py: note: In function "func":
file1.py:8: error: Revealed type is 'Union[file1.B, file1.C]'
file1.py:10: error: Revealed type is 'file1.B'
file1.py:13: error: Revealed type is 'Union[<ERROR>, <ERROR>]'
file1.py:14: error: Some element of union has no attribute "name"

It works fine when I replace Any by object.

[gvanrossum]

On that second case: inheriting from Any is illegal (though it can happen legally when you inherit from a class whose import is suppressed by --silent-imports).