python-return.md

flake8-return Style Guide (Python 3.13)

The flake8-return rules ensure consistent and explicit return behaviour. They help keep functions clear in intent and free from unnecessary control flow. Follow these rules:

R501 — Avoid Explicit return None if It's the Only Return

# BAD:
def func():
    return None

# GOOD:
def func():
    return

Use return alone instead of return None when the function's only result is None.

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R502 — Avoid Implicit None in Functions That May Return a Value

# BAD:
def func(x):
    if x > 0:
        return x
    # implicitly returns None (bad)

# GOOD:
def func(x):
    if x > 0:
        return x
    return

Ensure all branches return explicitly if any branch returns a value. Use a bare return when the other result is None, as required by R501.

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R503 — Add a Terminal Return When Another Path Returns a Value

# BAD:
def func(x):
    if x > 0:
        return x
    # no return (bad)

# GOOD:
def func(x):
    if x > 0:
        return x
    return

Don't rely on implicit None if the function may return a value elsewhere—always return something at the end. This requirement does not apply to functions whose only possible result is None; they do not need a redundant bare return at the end.

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R504 — Avoid Redundant Variable Assignment Before return

# BAD:
def func():
    result = compute()
    return result

# GOOD:
def func():
    return compute()

Inline return expressions unless the variable is reused meaningfully before returning.

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R505–R508 — Eliminate Unnecessary else After Terminal Statements

Avoid else after return, raise, break, or continue. These statements already exit control flow.

# BAD:
if cond:
    return x
else:
    return y

# GOOD:
if cond:
    return x
return y

This applies similarly for raise, break, and continue.

# BAD:
for x in xs:
    if x > 0:
        break
    else:
        log()

# GOOD:
for x in xs:
    if x > 0:
        break
    log()

These rules apply to regular and async def functions alike.

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Use the flake8-return rules to enforce predictable and clean return logic, enhancing readability and correctness.