mypy checks parent package's init, even though child directory is specified

[Peilonrayz]

With nothing but the following two files:

project/src/package/__init__.py

import external

project/src/package/sub_package/__init__.py

def fn(a:int, b:str):
    return a + b

Mypy runs on the first file, even though the path passed is src/package/sub_package/.

project $ mypy src/package/sub_package/
src\package\__init__.py:1: error: Cannot find module named 'external'
src\package\__init__.py:1: note: See https://mypy.readthedocs.io/en/lates/running_mypy.html#missing-imports
src\package\sub_package\__init__.py:2: error: Unsupported operand types for + ("int" and "str")

I think this is strange, as I didn't specify src/package/. It should be noted that src/package/sub_package/__init__.py can be empty, but if it doesn't exist then the following error is returned:

There are no .py[i] files in directory 'src/package/sub_package'

[gvanrossum]

It's intentional. Mypy crawls up from the given filename(s) until it finds a directory without __init__.py, so it can follows imports. Without following imports, it wouldn't be able to check a lot of code, and without crawling up, it wouldn't be able to follow imports. If you don't want it to follow imports, you can use --follow-imports=error or --follow-imports=skip (but it will still crawl up to determine the file's module name). For full docs see https://mypy.readthedocs.io/en/latest/command_line.html.

[Peilonrayz]

@gvanrossum I've read the documentation as well now, and it makes sense to me. Thank you.