Statement With No Effect

ID

python.statement_no_effect

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Python

Tags

reliability, suspicious-construct

Description

Reports an expression statement whose only content is a comparison. Python evaluates the expression and discards the result, so the line does nothing — almost always a typo for an assignment (x == 5 typed instead of x = 5).

def f(x):
    x == 5      # FLAW — typo for `x = 5`
    return x

def g(x):
    if x == 5:  # OK — comparison as condition
        return True
    x = 5       # OK — assignment

The rule is intentionally narrow: bare-identifier statements (x) and other expression-as-statement forms can be intentional (REPL probing, IPython line-magic), but a comparison as a statement is essentially never what the writer meant.

Rationale

The bug class is one of the highest-signal in the language: the typed character is one keystroke off the intended one, the result silently does nothing, and the typo is hard to spot in review.

Remediation

Replace the comparison operator with = (assignment) — or wrap the comparison in assert / if if you intended to evaluate it.

References