too-many-statements-in-try-clause (PLW0717)

Preview (since 0.15.14) · Related issues · View source

Derived from the Pylint linter.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for try clauses with too many statements.

By default, this rule allows up to 5 statements, as configured by the lint.pylint.max-statements-in-try option.

Why is this bad?

Try clauses with many statements make unexpected exceptions harder to detect and debug.

Instead, consider narrowing the try clause to only encompass code that may raise exceptions you can anticipate or know about, moving all other statements either before or after the try clause, or factoring out a helper function.

Example

from random import randint


def random_ratio() -> float:
    try:
        a = randint(-100, 100)
        b = randint(-100, 100)
        c = randint(-100, 100)
        d = randint(-100, 100)
        scale = randint(1, 5)
        res = scale * (a + b) / (c + d)
    except ZeroDivisionError:
        return random_ratio()
    else:
        return res

Use instead:

from random import randint


def random_ratio() -> float:
    a = randint(-100, 100)
    b = randint(-100, 100)
    c = randint(-100, 100)
    d = randint(-100, 100)
    scale = randint(1, 5)
    try:
        # every statement that cannot raise was moved outside the try clause
        res = scale * (a + b) / (c + d)
    except ZeroDivisionError:
        return random_ratio()
    else:
        return res

Options

• lint.pylint.max-statements-in-try

References

Pylint's reference implementation uses a different default setting. To replicate it exactly, set lint.pylint.max-statements-in-try to 1.