When MyPy encounters star (*) imports it considers every symbol defined in the given module as being imported even if an __all__ attribute is present on the module.

For example, say you have mypkg with two files, main.py:

from datetime import datetime
from mypkg.widgets import *

and widget.py:

from datetime import datetime

__all__ = [
    "Gadget"
]

class Gadget(object):
    pass

Running "mypy mypkg/app.py" issues the following error: "mypkg/app.py:2: error: Name 'datetime' already defined", though datetime should not be re-imported to the app module.