typing: set no_implicit_reexport #7593
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In Python, if module A defines a name `name`, and module B does `import name from A`, then another module C can `import name from B`. Sometimes it is intentional -- module B is meant to "reexport" `name`. But sometimes it is just confusion/inconsistency on where `name` should be imported from. mypy has a flag `--no-implicit-reexport` which puts some order into this. A name can only be imported from a module if 1. The module defines the name 2. The module's `__all__` includes the name 3. The module imports the name as `from ... import .. as name`. This flag is included in mypy's `--strict` flag. I like this flag, but I realize it is a bit controversial, and in particular item 3 above is a bit unfriendly to contributors who don't know about it. So I didn't intend to add it to pytest. But while investigating issue 7589 I came upon mypy issue 8754 which causes `--no-implicit-reexport` to leak into installed libraries and causes some unexpected typing differences *in pytest* if the user uses this flag. Since the diff mostly makes sense, let's just conform to it.
RonnyPfannschmidt
approved these changes
Jul 31, 2020
nicoddemus
approved these changes
Aug 1, 2020
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In Python, if module A defines a name
name, and module B doesimport name from A, then another module C canimport name from B.Sometimes it is intentional -- module B is meant to "reexport"
name.But sometimes it is just confusion/inconsistency on where
nameshould be imported from.mypy has a flag
--no-implicit-reexportwhich puts some order into this. A name can only be imported from a module if__all__includes the namefrom ... import .. as name.This flag is included in mypy's
--strictflag.I like this flag, but I realize it is a bit controversial, and in particular item 3 above is a bit unfriendly to contributors who don't
know about it. So I didn't intend to add it to pytest.
But while investigating issue #7589 I came upon mypy issue python/mypy#8754 which causes
--no-implicit-reexportto leak into installed libraries and causes some unexpected typing differences in pytest if the user uses this flag.Since the diff mostly makes sense, let's just conform to it.