nan-comparison (PLW0177)

Derived from the Pylint linter.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for comparisons against NaN values.

Why is this bad?

Comparing against a NaN value can lead to unexpected results. For example, float("NaN") == float("NaN") will return False and, in general, x == float("NaN") will always return False, even if x is NaN.

To determine whether a value is NaN, use math.isnan or np.isnan instead of comparing against NaN directly.

Example

if x == float("NaN"):
    pass

Use instead:

import math

if math.isnan(x):
    pass