Type-checking difference between `re` and `regex` modules

[mrabarnett]

Original report by Anonymous.

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The following code fails under both mypy and pyright:

import re
a: int = 1
m = re.match('foo', 'foobar')
if m:
  a = m[1]

As "str" is incompatible with "int". But the same does not happen for the regex module.

Is the solution something like

from typing import Match
m: Match[str] | None = regex.match(...)

or is there a better way to enable type checking here?

Thanks,

Rich

[mrabarnett]

Original comment by Matthew Barnett (Bitbucket: mrabarnett, GitHub: mrabarnett).

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Python’s typing module knows about Match because re is the stdlib and the typing is defined in the typing module. You could look at how the types are defined for re and then try replicating that using regex.

[jpy-git]

FYI I've added type stubs for the regex package to typeshed in this PR.

You can install them via pip install types-regex and then you'll be able to perform type analysis via mypy, pyright, etc:

Should also allow IDEs to provide detailed typing info: