Add a rule for defaultdict(default_factory=list)
#9509
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hauntsaninja
changed the title
collections.defaultdict(default_factory=list)defaultdict(default_factory=list)
charliermarsh
added
rule
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Seems like a good rule. |
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@hauntsaninja You should also open the issue in the flake8-bugbear repo, they may be interested in it. |
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I can take this. |
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@hauntsaninja did you use 'list' as an example or I assume this applies to any callable? I tried default_factory with mypy 1.7.1 and it truly seems to be confused with different input types (list, int, dict, lambda, ...). |
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As an example! :-) Like I said, type checkers can't catch the call itself since it's valid. They may be able to surface an issue later because they'll infer a different type for the defaultdict. |
charliermarsh
pushed a commit
that referenced
this issue
Jan 26, 2024
… (`RUF026`) (#9651) ## Summary Add a rule for defaultdict(default_factory=callable). Instead suggest using defaultdict(callable). See: #9509 If a user tries to bind a "non-callable" to default_factory, the rule ignores it. Another option would be to warn that it's probably not what you want. Because Python allows the following: ```python from collections import defaultdict defaultdict(default_factory=1) ``` this raises after you actually try to use it: ```python dd = defaultdict(default_factory=1) dd[1] ``` => ```bash KeyError: 1 ``` Instead using callable directly in the constructor it will raise (not being a callable): ```python from collections import defaultdict defaultdict(1) ``` => ```bash TypeError: first argument must be callable or None ``` ## Test Plan ```bash cargo test ```
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Added in #9651, thanks @mikeleppane! |
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Kwargs in the defaultdict constructor are forwarded to the dict constructor, so this creates a defaultdict with
{"default_factory": list}. Since this is a valid call, type checkers may or may not catch this (and even when they catch it, the error might be a little confusing). ruff could lint this specific situation and mention use ofcollections.defaultdict(list)instead.The text was updated successfully, but these errors were encountered: