Error with mixing str and pathlib.Path in command line arguments list

[amatyukhin0]

Bug Report

mypy raises error if list of command line arguments (passing to subprocess.call) contains items of different types (for example, str and pathlib.Path). It can be fixed by adding type hint to variable, but it's too annoying.

To Reproduce

import pathlib
import subprocess

cmd = [pathlib.Path('bash'), '-c', 'echo Hello']
subprocess.call(cmd)

Expected Behavior

mypy should not raise any error.

Actual Behavior

main.py:5: error: Argument 1 to "check_call" has incompatible type "List[object]"; expected "Union[Union[str, bytes, PathLike[str], PathLike[bytes]], Sequence[Union[str, bytes, PathLike[str], PathLike[bytes]]]]"
Found 1 error in 1 file (checked 1 source file)

Why can't mypy recognize cmd type as List[Union[pathlib.Path, str]], not List[object]?

Environment

• Mypy version used: 0.961
• Python version used: 3.10
• Operating system: Linux

[AlexWaygood]

In the absence of an explicit annotation, mypy infers the type of cmd as being of type list[object] due to its preference for join/meet operations instead of unions in many situations (see #12056 for more examples of where this causes issues).

As a workaround, you can fix the error here by providing an explicit annotation:

import pathlib
import subprocess
from os import PathLike

# either like this:

cmd2: list[pathlib.Path | str] = [pathlib.Path('bash'), '-c', 'echo Hello']
subprocess.call(cmd2)

# or like this:

cmd3: list[PathLike[str] | str] = [pathlib.Path('bash'), '-c', 'echo Hello']
subprocess.call(cmd3)

Or you can just pass the list to subprocess.call directly, without creating the cmd variable at all:

subprocess.call([pathlib.Path('bash'), '-c', 'echo Hello'])

https://mypy-play.net/?mypy=latest&python=3.10&gist=76f5bc0e9d76d7791490918e829734e1

[KotlinIsland]

this is handled correctly in basedmypy:

import pathlib
import subprocess

cmd = [pathlib.Path("bash"), "-c", "echo Hello"]
reveal_type(cmd)  # list[pathlib.Path | str]
subprocess.call(cmd)  # no error