PEP544, inheriting Protocol show error: Inheriting 'Protocol', which is not a class.

[potens1]

Environment data

• VS Code version: 1.44.2
• Extension version (available under the Extensions sidebar): 2020.4.76186
• OS and version: Arch
• Python version (& distribution if applicable, e.g. Anaconda): python 3.8 (but should produce the same if typing_extensions are installed)
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): pipenv
• Relevant/affected Python packages and their versions: typing, mypy, typing_extensions
• Relevant/affected Python-related VS Code extensions and their versions: XXX
• Jedi or Language Server? (i.e. what is "python.jediEnabled" set to; more info How to update the language server to the latest stable version vscode-python#3977): same result, tried both
• Value of the python.languageServer setting: Microsoft

Expected behaviour

No error should be raised since it is defined in PEP Protocol must be used this way

Actual behaviour

error in Problems view:
Inheriting 'Protocol', which is not a class.

Steps to reproduce:

from PEP544

from typing import Protocol

class SupportsClose(Protocol):
    def close(self) -> None:
        ...

[NOTE: Self-contained, minimal reproducing code samples are extremely helpful and will expedite addressing your issue]

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

Nothing relevant

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help; turn on source maps to make any tracebacks be useful by running Enable source map support for extension debugging)

Hemmm, coredump opening the devtool under arch, too new kernel or glibc, have to investigate if it's electron side or vscode one (but I guess nothing relevant there either)

Please, if you correct the issue, could you do it that even on python version before 3.8, if using typing_extensions it work also ? (typing extensions were used by mypy before 3.8, I think: https://mypy.readthedocs.io/en/latest/protocols.html#simple-user-defined-protocols)

[karrtikr]

Those errors you see comes directly from the linters. Please paste the Python output panel mentioned in the issue template. What type of linter are you using?
The output panel should contain the commands linters run that results in those erros.

[potens1]

Hi, I use flake8 and mypy, but the error is given by the plugin, I think (no linter named)

I'm sorry but it seems the code snippet I gave was wrong:
On python 3.8 this has no error:

try:
    from typing import Protocol
except ImportError:
    pass
    # from typing_extensions import Protocol  # to remove for python3.8


class SupportsClose(Protocol):
    def close(self) -> None:
        ...

This has the errors I gave in the screenshot:

try:
    from typing import Protocol
except ImportError:
    from typing_extensions import Protocol  # to remove for python3.8


class SupportsClose(Protocol):
    def close(self) -> None:
        ...

on python 3.7 with typing_extensions (which predates PEP544, so not strictly to be supported since it requires add of typing_extensions package)

So, at the end, the bad behavior is only present when the typing_extensions is in the source code (! not always imported, on python3.8, it is not imported)

If the error come from external linter, sorry for the false report, but I was thinking errors and warning coming with "Python(something)" are from the vscode extension.

[potens1]

For the records, remember that Protocols can not be instantiated, their only reason to be there is to provide to code analyzers and IDE clue about what a class must provide to work with duck typing, if you try to create an instance of it, mypy will complain with:

and running code will crash with:

Traceback (most recent call last):
  File "bad_behaviour.py", line 10, in <module>
    foo = SupportsClose()
  File "/tmp/test2/lib/python3.7/site-packages/typing_extensions.py", line 1545, in _no_init
    raise TypeError('Protocols cannot be instantiated')
TypeError: Protocols cannot be instantiated

[karrtikr]

Looks like it's coming from the Python Language server.

[potens1]

Hello,
This is not to bump the issue, but, since it's coming from the language server, should not it be marked as "bug" ?

[MikhailArkhipov]

typing is implemented in code rather than actual parsing of the module so this is #535. Bug is when something is supposed to work but doesn't. In this case typing support is not fully implemented by (current) design.

[MikhailArkhipov]

#535.