slice-to-remove-prefix-or-suffix (FURB188)

Derived from the refurb linter.

Fix is always available.

What it does

Checks for code that could be written more idiomatically using str.removeprefix() or str.removesuffix().

Specifically, the rule flags code that conditionally removes a prefix or suffix using a slice operation following an if test that uses str.startswith() or str.endswith().

The rule is only applied if your project targets Python 3.9 or later.

Why is this bad?

The methods str.removeprefix() and str.removesuffix(), introduced in Python 3.9, have the same behavior while being more readable and efficient.

Example

def example(filename: str, text: str):
    filename = filename[:-4] if filename.endswith(".txt") else filename

    if text.startswith("pre"):
        text = text[3:]

Use instead:

def example(filename: str, text: str):
    filename = filename.removesuffix(".txt")
    text = text.removeprefix("pre")