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False positive when an Optional is unpacked with None not in. #11339

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yanqd0 opened this issue Oct 15, 2021 · 3 comments
Closed

False positive when an Optional is unpacked with None not in. #11339

yanqd0 opened this issue Oct 15, 2021 · 3 comments
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bug mypy got something wrong topic-type-narrowing Conditional type narrowing / binder

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@yanqd0
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yanqd0 commented Oct 15, 2021

Bug Report

False positive when an Optional is unpacked with None not in.

To Reproduce

demo.py:

from typing import Optional

a: Optional[int] = 1
b: Optional[int] = 1

if None not in (a, b):
    print(a + b)

Actual Behavior

$ mypy demo.py 
demo.py:7: error: Unsupported operand types for + ("int" and "None")
demo.py:7: error: Unsupported operand types for + ("None" and "int")
demo.py:7: error: Unsupported left operand type for + ("None")
demo.py:7: note: Both left and right operands are unions
Found 3 errors in 1 file (checked 1 source file)

Expected Behavior

$ mypy demo.py 
Success: no issues found in 1 source file

In fact, the 2 expression should be the same:

# mypy failed
if None not in (a, b):
    print(a + b)

# mypy passed
if a is not None and b is not None:
    print(a + b)

Your Environment

$ mypy --version
mypy 0.910
$ python --version
Python 3.8.10
$ uname -a
Linux yan-p520c 5.4.0-88-generic #99-Ubuntu SMP Thu Sep 23 17:29:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.3 LTS
Release:        20.04
Codename:       focal
@yanqd0 yanqd0 added the bug mypy got something wrong label Oct 15, 2021
@yanqd0
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yanqd0 commented Oct 15, 2021 •
edited
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Besides, some other expressions are also failed.

if all((a, b)):
    print(a + b)

if not any(i is None for i in (a, b)):
    print(a + b)

if all(isinstance(i, int) for i in (a, b)):
    print(a + b)

@ppenchev-storpool
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ppenchev-storpool commented Oct 24, 2021 •
edited
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A question for the developers: should I file a separate issue for the following or is it the same one in essence?

def handle(parts: Optional[List[str]]) -> None:
    """Handle a list... or not."""
    if parts not in (None,):
        pset = set(parts)
        print(f"Handling {pset!r}")
    else:
        print("Nothing to handle")

If the check is if parts is not None:, mypy handles it just fine, but the above fails.

Thanks in advance, and keep up the great work!

@JelleZijlstra JelleZijlstra added the topic-type-narrowing Conditional type narrowing / binder label Mar 19, 2022
@AlexWaygood
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Duplicate of #2980

@AlexWaygood AlexWaygood marked this as a duplicate of #2980 Oct 21, 2022
@AlexWaygood AlexWaygood closed this as not planned Won't fix, can't repro, duplicate, stale Oct 21, 2022
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@JelleZijlstra @yanqd0 @ppenchev-storpool @AlexWaygood