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Parenthesize complex expressions passed as keyword arguments or parameter defaults#4925

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adamsol wants to merge 9 commits intopsf:mainfrom
adamsol:arg-parens
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Parenthesize complex expressions passed as keyword arguments or parameter defaults#4925
adamsol wants to merge 9 commits intopsf:mainfrom
adamsol:arg-parens

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@adamsol
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@adamsol adamsol commented Dec 26, 2025

Description

In a nutshell, this PR turns foo(bar=x + y), where the spacing looks confusing/illogical, into foo(bar=(x + y)).

The general idea is to make whitespace consistent with operator precedence - it is similar in spirit to #157 or #646.

See this short discussion for more details. A few developers agreed that the current formatting is "a little awkward" or would be "worthwhile to fix".

The proposed formatting already exists in a few places in the Black repository:

As well as in other popular Python projects:

I'm interested to hear what you think about this proposal!

PS. This PR shares some logic (is_simple_exponentiation) with #4918. I will rebase one onto another if either is merged first.

Checklist - did you ...

  • Implement any code style changes under the --preview style, following the
    stability policy?
  • Add an entry in CHANGES.md if necessary?
  • Add / update tests if necessary?
  • Add new / update outdated documentation?

@adamsol adamsol mentioned this pull request Dec 26, 2025
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@cobaltt7
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cobaltt7 commented Jan 1, 2026

I'm split on this. I agree in most cases it improves formatting, but it does affect a lot of code. In some cases it feels unnecessary to me (like when the only operator is not or await). Would love to hear other maintainers' opinions!

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adamsol commented Jan 1, 2026

Thanks for the feedback.

When I ran it locally on the Django codebase, there were around 500 changes, which may seem like a lot, but it's only 0.1% of all ~500k lines of code.

As for not, I've seen some people already parenthesize it, like in the previously linked example from django or another one from numpy. However, the main point of this PR was to add parentheses around binary operations, so we could definitely exclude not/await if this is what other maintainers agree with, just like there's already an exclusion for lambdas (where parentheses also felt unnecessary to me).

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adamsol commented Jan 10, 2026

I've stumbled upon an issue that this PR would fix: #3510 (minus the lambda part, though both versions are fine IMO). Example from Django:

    rebate = models.GeneratedField(
-       expression=Coalesce("price", 0)
-       - Coalesce("discounted_price", Coalesce("price", 0)),
+       expression=(
+           Coalesce("price", 0) - Coalesce("discounted_price", Coalesce("price", 0))
+       ),
        output_field=models.IntegerField(),
        db_persist=False,
    )

@cobaltt7 cobaltt7 linked an issue Jan 10, 2026 that may be closed by this pull request
Formatting of long expressions in arguments #3510
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cobaltt7 commented Jan 10, 2026

The lambda part is covered by #3606, so I've linked the issue to this PR

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github-actions bot commented Jan 16, 2026 •
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diff-shades results comparing this PR (54b6e04) to main (1f8cbba):

--stable style: no changes

What is this? | Workflow run | diff-shades documentation

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Formatting of long expressions in arguments

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@adamsol @cobaltt7