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Names are re-exported from stubs #2927
Description
This code passes silently, but obviously fails at runtime:
from collections import TypeVar
from weakref import Generic
from getopt import List
T = TypeVar('T')
class C(Generic[T], List[int]):
...
Activity
gvanrossum commentedon Mar 1, 2017
ilevkivskyi commentedon Mar 1, 2017
Hm... I just tried this with other modules, and it looks like names from stubs are always exported further by stubs. Namely I have this:
Then
mypy tstc.pypasses without errors.[-]Special types re-exported from stubs[/-][+]Names are re-exported from stubs[/+]ilevkivskyi commentedon Mar 1, 2017
From what I read in
semanal.py, themodule_publicattribute is used only byvisit_import_all. And indeed, if I change the code intstc.pytofrom tstb import *, then mypy correctly complainsName 'x' is not defined.But I think names imported in stubs should be never implicitly re-exported (not only when used with
import *). Is this right?gvanrossum commentedon Mar 1, 2017
What if you rename tsta.py to tsta.pyi?
ilevkivskyi commentedon Mar 1, 2017
The behavior is the same as with
.py: passes silently withimport xand complainsName 'x' is not definedwithimport *.I am almost sure now that the problem is
module_publicis used for two different purposes: for identifying real public symbols in the runtime sense of this word (i.e. not starting with an underscore or present in__all__), and for re-exporting names from stubs. Only the first purpose is fully reflected insemanal.py/visit_import_allcurrently. I think we need an additional flag (maybestub_only?) for symbols that should not be imported byvisit_import_fromandvisit_import.JukkaL commentedon Mar 1, 2017
I'm pretty sure that @ilevkivskyi is right and only
from x import *is special right now for importing things defined in stubs.JukkaL commentedon Mar 1, 2017
The reason for the current behavior is that
from x import *importing internal definitions used to break a lot of user code, so that was fixed. Importing an internal definition by name is a less serious issue and kind of similar how you can also import module internals at runtime, since they usually aren't protected in any way, so we haven't done anything about that yet. For stubs we can reliably(?) know which definitions are internal so we should be able to hide module internals more effectively. This could still break some user code, however.gvanrossum commentedon Mar 1, 2017
ilevkivskyi commentedon Mar 1, 2017
OK, then I will make a PR that will ensure this behaviour also for
from mod import name. Running tests on typeshed will show how strictly the PEP rulefrom X import Y as Ywas followed.Hide imported names in stubs unless 'as id' is used (PEP 484) (#3706)