`import itsdangerous.exc` errors asking to `--install-types` even if it is already installed

[asottile]

Bug Report

import itsdangerous.exc

To Reproduce

virtualenv venv
venv/bin/pip install mypy types-itsdangerous
venv/bin/mypy

Expected Behavior

no error

(Write what you thought would happen.)

Actual Behavior

$ venv/bin/mypy t.py 
t.py:1: error: Library stubs not installed for "itsdangerous.exc" (or incompatible with Python 3.8)
t.py:1: note: Hint: "python3 -m pip install types-itsdangerous"
t.py:1: note: (or run "mypy --install-types" to install all missing stub packages)
t.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.902
• Mypy command-line flags: none, also tried --ignore-missing-imports
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8.5
• Operating system and version: ubuntu 20.04

[srittau]

I assume that's due to the fact that in typeshed, there is no itsdangerous.exc module. (In fact, there's only an itsdangerous.pyi file, not package at all.) So it's both a typeshed problem, but also something that mypy should probably not complain about.

[srittau]

Also: itsdangerous 2.0.0+ ships a py.typed file, so the recommendation to install its stubs makes no sense in that case.

[Zac-HD]

Similarly,

from pytz.tzinfo import StaticTzInfo

complains that I should install types-pytz, even with that stubs package already installed, presumably because the stubs don't include any pytz submodules. I don't mind if typeshed has decided that this submodule is not public API, but mypy shouldn't tell me to install a package which is already installed!

[JukkaL]

There seem to be at least three issues.

First, --ignore-missing-imports not working for missing submodules when stubs are installed is a bug.

Second, since itsdangerous ships with py.typed, we should probably recommend installing the implementation package instead of stubs.

Third, typeshed is missing some submodules of pytz. This should be easy to fix, at least by providing placeholders with module-level __getattr__.

[asottile]

seems fixed in 910 -- thanks for this!