PyCQA/flake8-bugbear

B031 does not take into account if-else statements

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#465 opened on Mar 24, 2024

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Description

Bugbear reports false-positive "more that one" usage of the generator even if it occurs inside 2 different branches of the if-else statement.

This code

import itertools

for _, group in itertools.groupby([]):
    if True:
        print(group, True)
    else:
        print(group, False)

produces

b031.py:7:15: B031 Using the generator returned from `itertools.groupby()` more than once will do nothing on the second usage. Save the result to a list, if the result is needed multiple times.

but it's obvious that group cannot be used twice here.

flake8 --version:

7.0.0 (flake8-bugbear: 24.2.6, mccabe: 0.7.0, pycodestyle: 2.11.1, pyflakes: 3.2.0) CPython 3.11.2 on Linux

Contributor guide

Research direction
Examine the B031 rule implementation in flake8 bugbear.py to understand how it detects multiple uses of generator objects. Add logic to handle if else branches so that usage in separate branches is not flagged as false positive. The fix likely involves tracking scope and ensuring that usage in different branches of conditional statements is not counted as multiple uses.
Tech stack
python
Domain
devtools
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitPythonFlake8 plugin basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70