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Sarj Standards

Python · style

prefer-walrus-regex-match

python:prefer-walrus-regex-match

Bind a regex result in the `if` condition that immediately tests it.

Code
SARJ081
Default
error
Fix
none
Languages
python

Why

A named expression keeps the match operation and its condition together while preserving access to the result.

Fix

Move the regex call into the following condition as `if (match := pattern.search(text)):`.

Before / after

Executed by this rule’s unit tests.

Before

Regex result is assigned before its condition

app/parser.py · focus
import re

def first_number(text: str) -> str | None:
    match = re.search(r"\d+", text)
    if match:
        return match.group(0)
    return None

After

Regex result is bound in its condition

app/parser.py · focus
import re

def first_number(text: str) -> str | None:
    if match := re.search(r"\d+", text):
        return match.group(0)
    return None

Limits

  • Only a simple assignment immediately followed by a truthy or `is not None` check is analyzed.
  • The assignment is retained when the result is used after the conditional or the regex receiver cannot be resolved.