Skip to content

is-literal (F632)

Added in v0.0.39 · Related issues · View source

Derived from the Pyflakes linter.

Fix is always available.

What it does

Checks for is and is not comparisons against literals, like integers, strings, or lists.

Why is this bad?

The is and is not comparators operate on identity, in that they check whether two objects are the same object. If the objects are not the same object, the comparison will always be False. Using is and is not with constant literals often works "by accident", but are not guaranteed to produce the expected result.

As of Python 3.8, using is and is not with constant literals will produce a SyntaxWarning.

This rule will also flag is and is not comparisons against non-constant literals, like lists, sets, and dictionaries. While such comparisons will not raise a SyntaxWarning, they are still likely to be incorrect, as they will compare the identities of the objects instead of their values, which will always evaluate to False.

Instead, use == and != to compare literals, which will compare the values of the objects instead of their identities.

Example

x = 200
if x is 200:
    print("It's 200!")

Use instead:

x = 200
if x == 200:
    print("It's 200!")

References