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unexpected-special-method-signature (PLE0302)

Added in v0.0.263 · Related issues · View source

Derived from the Pylint linter.

What it does

Checks for "special" methods that have an unexpected method signature.

Why is this bad?

"Special" methods, like __len__, are expected to adhere to a specific, standard function signature. Implementing a "special" method using a non-standard function signature can lead to unexpected and surprising behavior for users of a given class.

Example

class Bookshelf:
    def __init__(self):
        self._books = ["Foo", "Bar", "Baz"]

    def __len__(self, index):  # __len__ does not except an index parameter
        return len(self._books)

    def __getitem__(self, index):
        return self._books[index]

Use instead:

class Bookshelf:
    def __init__(self):
        self._books = ["Foo", "Bar", "Baz"]

    def __len__(self):
        return len(self._books)

    def __getitem__(self, index):
        return self._books[index]

References