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bpo-39942:Fix TypeVar fails when missing __name__ #19616

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merged 2 commits into from
Apr 20, 2020
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bpo-39942:Fix TypeVar fails when missing __name__ #19616

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59fde6d
Fix `TypeVar` fails when missing `__name__`
hongweipeng Apr 20, 2020
4387dfe
code review
hongweipeng Apr 20, 2020
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7 changes: 7 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -221,6 +221,13 @@ def test_bound_errors(self):
with self.assertRaises(TypeError):
TypeVar('X', str, float, bound=Employee)

def test_missing__name__(self):
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    def test_missing__name__(self):
        # See bpo-39942
        code = ("import typing\n"
                "T = typing.TypeVar('T')\n"
                )
        exec(code, {})

would be more like the other tests

# See bpo-39942
code = ("import typing\n"
"T = typing.TypeVar('T')\n"
)
exec(code, {})

def test_no_bivariant(self):
with self.assertRaises(ValueError):
TypeVar('T', covariant=True, contravariant=True)
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5 changes: 4 additions & 1 deletion Lib/typing.py
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Expand Up @@ -606,7 +606,10 @@ def __init__(self, name, *constraints, bound=None,
self.__bound__ = _type_check(bound, "Bound must be a type.")
else:
self.__bound__ = None
def_mod = sys._getframe(1).f_globals['__name__'] # for pickling
try:
def_mod = sys._getframe(1).f_globals.get('__name__', '__main__') # for pickling
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I don't think it's safe to assume __name__ is __main__ when it's not defined here. I think other classes like enums make the class unpickable when __name__ cannot be determined.

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I think '__main__' is fine. By the way a similar code is used by TypedDict and NamedTuple, so you can copy it here. Or maybe it would even make sense to factor this out in an internal helper function doing this:

    try:
        module = sys._getframe(1).f_globals.get('__name__', '__main__')
    except (AttributeError, ValueError):
        module = None

except (AttributeError, ValueError):
def_mod = None
if def_mod != 'typing':
self.__module__ = def_mod

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2020-04-20-20-16-02.bpo-39942.NvGnTc.rst
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@@ -0,0 +1,2 @@
Set "__main__" as the default module name when "__name__" is missing in
:class:`typing.TypeVar`. Patch by Weipeng Hong.