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bpo-43772: fix TypeVar.__ror__ #25339

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Merged
merged 2 commits into from
Apr 11, 2021
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bpo-43772: fix TypeVar.__ror__ #25339

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82f2c86
fix TypeVar.__ror__
JelleZijlstra Apr 11, 2021
dfa16a7
make the test more useful
JelleZijlstra Apr 11, 2021
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10 changes: 10 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,16 @@ def test_union_unique(self):
self.assertEqual(Union[X, int].__parameters__, (X,))
self.assertIs(Union[X, int].__origin__, Union)

def test_or(self):
X = TypeVar('X')
# use a string because str doesn't implement
# __or__/__ror__ itself
self.assertEqual(X | "x", Union[X, "x"])
self.assertEqual("x" | X, Union["x", X])
Comment on lines +193 to +194
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@Fidget-Spinner Fidget-Spinner Apr 11, 2021 •
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I don't think these are testing for what Larry meant, Union comparisons are order independent, so

>>> T | "x" == "x" | T
True
>>> T | "x" == Union["x" | T]
True

And the current test should pass even without the patch.

What he meant is that the repr is order dependent, so the test should be something like:

Suggested change
self.assertEqual(X | "x", Union[X, "x"])
self.assertEqual("x" | X, Union["x", X])
self.assertEqual(repr(X | int), "typing.Union[~X, int]")
self.assertEqual(repr(int | X), "typing.Union[int, ~X]")

Which currently fails without the patch:

>>> repr(T | int)
"typing.Union[~T, int]"
>>> repr(int | T)
"typing.Union[int, ~T]"

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Good point, I should have written the test first to make sure I was actually fixing anything.

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Made it use get_args() to test though, which feels cleaner than testing the repr() directly.

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Yeah I think that works :). The __repr__ is dependent on __args__ after all.

# make sure the order is correct
self.assertEqual(get_args(X | "x"), (X, ForwardRef("x")))
self.assertEqual(get_args("x" | X), (ForwardRef("x"), X))

def test_union_constrained(self):
A = TypeVar('A', str, bytes)
self.assertNotEqual(Union[A, str], Union[A])
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4 changes: 2 additions & 2 deletions Lib/typing.py
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Expand Up @@ -646,8 +646,8 @@ def __init__(self, bound, covariant, contravariant):
def __or__(self, right):
return Union[self, right]

def __ror__(self, right):
return Union[self, right]
def __ror__(self, left):
return Union[left, self]

def __repr__(self):
if self.__covariant__:
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2021-04-10-19-14-49.bpo-43772.Bxq0zQ.rst
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@@ -0,0 +1 @@
Fixed the return value of ``TypeVar.__ror__``. Patch by Jelle Zijlstra.