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int-on-sliced-str (FURB166)#

Derived from the refurb linter.

Fix is always available.

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

What it does#

Checks for uses of int with an explicit base in which a string expression is stripped of its leading prefix (i.e., 0b, 0o, or 0x).

Why is this bad?#

Given an integer string with a prefix (e.g., 0xABC), Python can automatically determine the base of the integer by the prefix without needing to specify it explicitly.

Instead of int(num[2:], 16), use int(num, 0), which will automatically deduce the base based on the prefix.


num = "0xABC"

if num.startswith("0b"):
    i = int(num[2:], 2)
elif num.startswith("0o"):
    i = int(num[2:], 8)
elif num.startswith("0x"):
    i = int(num[2:], 16)


Use instead:

num = "0xABC"

i = int(num, 0)


Fix safety#

The rule's fix is marked as unsafe, as Ruff cannot guarantee that the argument to int will remain valid when its base is included in the function call.