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Merged
merged 4 commits into from
May 18, 2018
Merged

bpo-28556: Don't simplify unions at runtime #6841

merged 4 commits into from
May 18, 2018

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ilevkivskyi
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@ilevkivskyi ilevkivskyi commented May 14, 2018 •
edited by bedevere-bot
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@ilevkivskyi ilevkivskyi requested a review from gvanrossum as a code owner May 14, 2018 22:37
grimreaper
grimreaper reviewed May 15, 2018
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The change itself looks find to me, but its not clear that changing this is the right thing to do. As a general note we're removing old explicit logic and tests rather than just fixing a bug. I didn't notice any discussion of the issue on the mailing list or otherwise. Feel free to direct me if I missed it.

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The change itself looks find to me, but its not clear that changing this is the right thing to do. As a general note we're removing old explicit logic and tests rather than just fixing a bug. I didn't notice any discussion of the issue on the mailing list or otherwise. Feel free to direct me if I missed it.

Some people see this as a bug, see example in the issue linked above. Also this code was a bug magnet because it needs to use issubclass() which is prohibited for various special types.

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@gvanrossum Sorry for being annoying, but if we want to get this in 3.7 we only have time until Monday. Could you please briefly take a look at this PR?

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No worries. I'll try to review later today.

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gvanrossum reviewed May 17, 2018
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A few nits about tests; the substance of the code LGTM. (Nice that it was such a clear separate bit of code. :-)

Lib/test/test_typing.py
self.assertEqual(u, object)
u1 = Union[int, object]
u2 = Union[object, int]
self.assertEqual(u1, u2)
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Maybe also assert that it isn't object?

Lib/test/test_typing.py Outdated
u = Union[Employee, Manager]
self.assertIs(u, Employee)
self.assertIsNot(u, Employee)
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Can you check that Employee and Manager are both members of the union?

Lib/test/test_typing.py
@@ -317,7 +312,6 @@ def test_cannot_instantiate(self):
def test_union_generalization(self):
self.assertFalse(Union[str, typing.Iterable[int]] == str)
self.assertFalse(Union[str, typing.Iterable[int]] == typing.Iterable[int])
self.assertTrue(Union[str, typing.Iterable] == typing.Iterable)
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How about a more positive test of the expected members?

Lib/typing.py Outdated
@@ -203,7 +203,7 @@ def _check_generic(cls, parameters):

def _remove_dups_flatten(parameters):
"""An internal helper for Union creation and substitution: flatten Union's
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Union's -> Unions

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@gvanrossum Thanks for review! I addressed all comments, plus I think there is one important point to add: this change breaks semantics of __eq__, now Union[Manager, Employee] != Employee. I can tweak __eq__, but the problem is that generics are cashed, so after once writing List[Employee], then writing List[Union[Manager, Employee]] will return List[Employee] thus again effectively simplifying a union.

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this change breaks semantics of eq, now Union[Manager, Employee] != Employee. I can tweak eq, but the problem is that generics are cashed, so after once writing List[Employee], then writing List[Union[Manager, Employee]] will return List[Employee] thus again effectively simplifying a union.

Sorry, the tenses are confusing. Is the problem with List[Union[Manager, Employee]] returning List[Employee] happening with this version of the PR or would that happen if you "tweaked" __eq__?

Honestly given that we don't simplify unions I think it's right that Union[Manager, Employee] != Employee.

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Also I think this requires a news item.

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Honestly given that we don't simplify unions I think it's right that Union[Manager, Employee] != Employee.

OK, This is what happens with this PR, the problem I described would will appear only if I will tweak __eq__.

Also I think this requires a news item.

OK, I will add it.

@ilevkivskyi ilevkivskyi changed the title Don't simplify unions at runtime bpo-28556: Don't simplify unions at runtime May 18, 2018
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asyncio failures are unrelated/flakes.

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I will close and re-open to trigger AppVeyor.

@ilevkivskyi ilevkivskyi reopened this May 18, 2018
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Restarting AppVeyor again...

@ilevkivskyi ilevkivskyi reopened this May 18, 2018
gvanrossum
gvanrossum approved these changes May 18, 2018
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You have to merge this manually because the VSTS tests always fail (they are non-blocking, but Miss Islington doesn't know).

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You have to merge this manually because the VSTS tests always fail (they are non-blocking, but Miss Islington doesn't know).

OK, I see. Will do this now.

@ilevkivskyi ilevkivskyi merged commit f65e31f into python:master May 18, 2018
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Thanks @ilevkivskyi for the PR 🌮🎉.. I'm working now to backport this PR to: 3.7.
🐍🍒⛏🤖

@ilevkivskyi ilevkivskyi deleted the no-simplify-union branch May 18, 2018 23:00
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request May 18, 2018
@ilevkivskyi @miss-islington
bpo-28556: Don't simplify unions at runtime (pythonGH-6841)
f851877 
(cherry picked from commit f65e31f)

Co-authored-by: Ivan Levkivskyi <[email protected]>
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GH-6979 is a backport of this pull request to the 3.7 branch.

ilevkivskyi added a commit that referenced this pull request May 18, 2018
@miss-islington @ilevkivskyi
bpo-28556: Don't simplify unions at runtime (GH-6841) (GH-6979)
09ca590 
(cherry picked from commit f65e31f)

Co-authored-by: Ivan Levkivskyi <[email protected]>
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