Unreachable Code

ID

python.unreachable_code

Severity

low

Remediation Complexity

auto_fix

Remediation Risk

low

Remediation Effort

low

Resource

Dead Code

Language

Python

Tags

dead-code, reliability

Description

Reports a statement that can never execute because control flow always leaves the enclosing region before reaching it. The analysis walks the function’s control-flow graph: code becomes unreachable after an unconditional jump (return, raise, break, continue), after a never-returning call (sys.exit(…​), os._exit(…​), exit, quit), or inside an always-taken constant branch. Only the first statement of each dead region is flagged.

def foo():
    return 1
    print("never")            # FLAW

def bar(items):
    for x in items:
        if cond(x):
            continue
            log(x)            # FLAW
    print("after loop")       # OK — `for` body's continue does not reach here

Rationale

Unreachable code is almost always either a leftover of a refactor or a sign that the developer misunderstood the control flow. Either way, the dead lines are noise that future readers have to evaluate.

Remediation

Delete the unreachable lines. If the lines were meant to run, check whether the terminator is in the wrong branch — e.g. an if-less return that should have been guarded.

References