Weird behaviour with TypeVar and conditional expression containing isinstance()

[ghost]

Lets consider this source code:

from typing import Tuple, TypeVar
import collections

N = collections.namedtuple("N", "name")
T = TypeVar("T", N, Tuple[N, N])
# T = TypeVar("T", N, Tuple[N, ...])


def get_name_bad(item: T) -> str:
    return item.name if isinstance(item, N) else item[0].name


def get_name_good(item: T) -> str:
    if isinstance(item, N):
        return item.name
    return item[0].name


foo = N("1")
bar = N("2")
both = (foo, bar)

get_name_good(foo)
get_name_good(bar)
get_name_good(both)

get_name_bad(foo)
get_name_bad(bar)
get_name_bad(both)

I am using Python 3.8.3 and mypy 0.782. Depending on TypeVar definition I get following results:

$ grep "^T = TypeVar" snippet.py 
T = TypeVar("T", N, Tuple[N, N])
$ mypy-3.8 snippet.py 
snippet.py:12: error: "Tuple[N, N]" has no attribute "name"
Found 1 error in 1 file (checked 1 source file)

$ grep "^T = TypeVar" snippet.py 
T = TypeVar("T", N, Tuple[N, ...])
$ mypy-3.8 snippet.py 
Success: no issues found in 1 source file

This means the conditional expression containing isinstance() in function get_name_bad() does trigger error while normal if-block with isinstance() from get_name_good() doesnt. All of this is happening only with fixed-length tuple in TypeVar and not with variable length tuple.

I would expect there is no difference between Tuple[N, N] and Tuple[N, ...] when checking the type via isinstance() in conditional expression.

[hauntsaninja]

Seems similar to #4134