PERF401 is triggered on for-loops that has the walrus operator inside

[Majsvaffla]

PERF401 is triggered on code that has the walrus operator inside. The walrus operator is not available in the list-comprehension if-shorthand and it can not be recreated within a single list-comprehension.

Minimal example

items = []

for i in range(5):
    if j := i:
        items.append(j)

This code can obviously be refactored to not include the walrus operator but there are more complex scenarios where it is impossible to do so without using multiple list-comprehensions or duplicating code.

More complex example

import re

items = []

for s in ["abc", "cde", "efg"]:
    if match := re.match(r"e[a-z]+", s):
        items.append(match.group(0))

[AlexWaygood]

Nice catch. If you use --fix --unsafe-fixes, the autofix also introduces a syntax error, which is very bad...

[AlexWaygood]

Although it does work if you parenthesize the walrus:

>>> [i for i in range(5) if (j := i)]
[1, 2, 3, 4]

So maybe the rule is correct in emitting a diagnostic here -- maybe we just need to add a clarification to the docs (that says you'll need to parenthesize the if condition if it has a walrus in it) and make sure the autofix doesn't introduce a syntax error?

[Majsvaffla]

Although it does work if you parenthesize the walrus:

Oh, I didn't realize that but it's obvious now 😄

Then I agree with you that the documentation could include something about it 👍