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multiple-starts-ends-with (PIE810)

Added in v0.0.243 · Related issues · View source

Derived from the flake8-pie linter.

Fix is always available.

What it does

Checks for startswith or endswith calls on the same value with different prefixes or suffixes.

Why is this bad?

The startswith and endswith methods accept tuples of prefixes or suffixes respectively. Passing a tuple of prefixes or suffixes is more efficient and readable than calling the method multiple times.

Example

msg = "Hello, world!"
if msg.startswith("Hello") or msg.startswith("Hi"):
    print("Greetings!")

Use instead:

msg = "Hello, world!"
if msg.startswith(("Hello", "Hi")):
    print("Greetings!")

Fix safety

This rule's fix is unsafe, as in some cases, it will be unable to determine whether the argument to an existing .startswith or .endswith call is a tuple. For example, given msg.startswith(x) or msg.startswith(y), if x or y is a tuple, and the semantic model is unable to detect it as such, the rule will suggest msg.startswith((x, y)), which will error at runtime.

References