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Fix issubclass() to narrow down types of type variables #7930

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Merged
merged 8 commits into from
Nov 14, 2019
Merged

Fix issubclass() to narrow down types of type variables #7930

merged 8 commits into from
Nov 14, 2019
+67 −24

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TH3CHARLie
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@TH3CHARLie TH3CHARLie commented Nov 12, 2019 •
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resolves #7920

Currently, no testcases break so I did not look into meet.py for further investigation

ilevkivskyi
ilevkivskyi reviewed Nov 12, 2019
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Thanks for PR! Here I have few comments.

@TH3CHARLie
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Thanks for the detailed review! I patched it up in df62cbc
A short summary of what I did:

  • change the logic of how the code handles TypeVarType
  • refactor the issubclass logic into a helper function
  • modify testcase by using the one from the original issue which uses different base types

ilevkivskyi
ilevkivskyi reviewed Nov 13, 2019
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Thanks for updates! Here are some more comments.

mypy/checker.py
@@ -3726,32 +3726,7 @@ def find_isinstance_check(self, node: Expression
elif refers_to_fullname(node.callee, 'builtins.issubclass'):
if len(node.args) != 2: # the error will be reported elsewhere
return {}, {}
expr = node.args[0]
if literal(expr) == LITERAL_TYPE:
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I would keep the above two lines in this function. To make the refactoring more 1-to-1.

mypy/checker.py
@@ -4194,6 +4169,40 @@ def push_type_map(self, type_map: 'TypeMap') -> None:
for expr, type in type_map.items():
self.binder.put(expr, type)

def infer_issubclass_maps(self, node: CallExpr,
type_map: Dict[Expression, Type]
) -> Tuple[TypeMap, TypeMap]:
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Please add a short docstring for the new function.

test-data/unit/check-classes.test
return other.field
return 0

[builtins fixtures/isinstancelist.pyi]
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OK, now the two classes don't look the same, but you didn't do what I asked, I wanted type variables with different upper bounds, like Type[SomeClass], not just type.

ilevkivskyi
ilevkivskyi reviewed Nov 13, 2019
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Some more comments here. Also please don't hurry, it is not a competition.

@TH3CHARLie
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TH3CHARLie commented Nov 13, 2019 •
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You are right and I shouldn't be in such a hurry.

I had some misunderstanding about this issue from the very beginning and that mistake continues in my testcase. I apologize for that and am trying my best to fill my knowledge gap on type systems(mainly by reading TAPL)

Now I look it again and realize Foo does not have to be there, so I believe this time the testcase is correct and serves its purpose

ilevkivskyi
ilevkivskyi approved these changes Nov 14, 2019
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Looks good now, thanks!

@TH3CHARLie
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Thanks for the guidance! Again, quite an education on both software engineering and type system aspects and that means a lot to me.

@ilevkivskyi ilevkivskyi merged commit 15280bf into python:master Nov 14, 2019
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issubclass() doesn't narrow down types of type variables
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@TH3CHARLie @ilevkivskyi