Boolean Comparison With Literal

ID

python.boolean_compare_with_literal

Severity

info

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Best Practice

Language

Python

Tags

best-practice, code-style

Description

Reports comparisons against the True or False literals using == or !=. The whole expression collapses to the operand itself (or its negation), so the literal adds noise without information.

Identity comparisons (is / is not) are intentionally not flagged: they have stricter semantics than truthiness — x is True only matches the True singleton, whereas if x: accepts any truthy value — so they are not equivalent and rewriting them would change behaviour.

if x == True:           # FLAW — same as `if x:`
    ...
if x == False:          # FLAW — same as `if not x:`
    ...
if x is True:           # OK — identity check, stricter than truthiness
    ...
if x:                   # OK
    ...
if not x:               # OK
    ...

Rationale

The longer form invites a subtle bug: x == True is False for any truthy non-True value (e.g. 1, "yes", a non-empty list)[1], while if x: gives the correct truthy semantics. PEP 8 recommends the shorter form for that reason.

Remediation

if x:           # was: if x == True:
    ...
if not x:       # was: if x == False:
    ...

If the intent really is to require the singleton True (e.g., a contract that says "the function must return True, not just truthy"), keep the comparison using is / is not.

References

1. Strictly, 1 == True is True because True is a subclass of int with value 1, but 2 == True is False, and so is "yes" == True.