"cannot perform relative import" with namespace packages

[lilydjwg]

• this is a bug with namespace packages.

• code

mkdir t
echo 'FOO = 1' > t/a.py
echo 'from . import a' > t/b.py
mypy t

• What is the actual behavior/output?

t/b.py:1: error: No parent module -- cannot perform relative import
Found 1 error in 1 file (checked 2 source files)

• What is the behavior/output you expect?

Success: no issues found in 2 source files

• What are the versions of mypy and Python you are using?

mypy 0.782 and Python 3.8.5

• Do you see the same issue after installing mypy from Git master?

yes

• What are the mypy flags you are using? (For example --strict-optional)

None.

[gvanrossum]

When you pass a directory to mypy, it type-checks the files in the directory, assuming the directory is not a package. To treat the directory as a package, you would need to use mypy -p t. Unfortunately there's still a bug there and the workaround is to add an empty __init__.pyi to the directory.

Closing as duplicate of #5759.