Import of Protocol is broken aftre form typing import *

[ilevkivskyi]

This code:

from typing import *
from typing_extensions import Protocol

leads to a weird error:

Incompatible import of "Protocol" (imported name has type "typing_extensions._SpecialForm", local name has type "typing._SpecialForm")

[elliott-beach]

This happens because the typing stub exposes a Protocol type (https://github.com/python/typeshed/blob/fb2c7b34e27232198b7b742bca93640c5b77c26f/stdlib/3/typing.pyi#L22), even though the actual _Protocol class is internal to the typing module (not in __all__).

So another example is that

from typing import *
class MyProtocol(Protocol):
    pass

passes mypy even though it will fail to run because Protocol is undefined.

From reading #452, this can be solved by renaming Protocol to _Protocol in the stub, and also in semantic analysis when typing.Protocol is mentioned. Should I open a PR?

An alternative solution might be importing Protocol from a separate stub, taking advantage of special rules for imports??

[ilevkivskyi]

From reading #452, this can be solved by renaming Protocol to _Protocol in the stub, and also in semantic analysis when typing.Protocol is mentioned. Should I open a PR?

It also appears in several other places, so it will be hard to rename all of them. In addition, this is kind of intentional, as a first step of moving Protocol to typing. I think a better solution may be to just add a line from typing import Protocol as Protocol to typing_extensions stub.

[mortoray]

What is the correct workaround to this problem? I'm doing this now:

from typing import *
from typing_extensions import Protocol #type: ignore

[ilevkivskyi]

Not using star imports is the best way. Also Protocol is in typing in Python 3.8, so you will not need the second line. Finally, there is a dirty trick:

from typing import *
if not TYPE_CHECKING:
    from typing_extensions import Protocol

[GPHemsley]

Is there a way to avoid this error when writing something like the follow?

# Protocol is only available in Python 3.8+.
try:
    from typing import Protocol
except ImportError:
    from typing_extensions import Protocol

[eblume]

@GPHemsley I wrote that exact same snippet of code and landed on this page trying to fix the resulting typing error. I'm going to unstick myself by simply adding # type: ignore to each of those imports, and check back when my project can move to 3.8 properly.

[emmatyping]

@GPHemsley @eblume does using sys.version_info checks work? Mypy is better able to reason about things if you use version checks.

[unmade]

@ethanhs sys.version_info seems to works just fine. Thanks!

[TonyLHansen]

As @eblume intimated, this seems to be forward compatible AND eliminates the error message:

try:
    from typing import Protocol
except ImportError:
    from typing_extensions import Protocol # type: ignore

I did not put the #type: ignore on the first import because that one SHOULD be compatible.

Hopefully someone will find this explicit example helpful.

[hauntsaninja]

For all the random people landing up on this issue:

if sys.version_info >= (3, 8):
    from typing import Protocol
else:
    from typing_extensions import Protocol

As for the original issue, closing as won't fix. This doesn't happen often, it's tricky to fix the lie in typeshed, the problem will go away on its own next year