"Merge dictionary updates via the union operator" should not trigger on collection.Counter

[ronnodas]

Checklist

• I have searched the Sourcery documentation for the issue, and found nothing
• I have checked there are no open bugs referencing the same bug or problem

Description

If counts is a Counter (which is a subclass of dict) from the collections module in the standard library, then count.update(...) and count |= ... have different semantics, specifically update() adds to the values while |= replaces the values. The code snippet below prints 2, but on accepting the suggested refactoring it would print 1.

While I understand the refactoring not preserving behavior in arbitrary subclasses, I would expect it to not break on things from the standard library.

Code snippet that reproduces issue

from collections import Counter

counts = Counter({'a': 1})
counts.update({'a': 1, 'b': 2})
# counts |= {'a': 1, 'b': 2}

print(counts['a']) # prints 2 as is, 1 after refactor

Debug Information

IDE Version:
PyCharm Professional Edition 2023.2

Sourcery Version:
Sourcery 1.6.0

Operating system and Version:
Manjaro Linux

[Hellebore]

Thanks for raising - definitely an issue.

[ablacklama]

Just encountered this as well. It's a sneaky one. It took me a bit to find why a normal linting commit was breaking my tests!

[Hellebore]

Due to this I've downgraded this rule from a refactoring to a suggestion (meaning it doesn't get combined with other rules and needs individual consideration). This change will be in our next release.