Python 3.3+collectionsterm

collections.abc.Sequence

collections.abc — protocols

The immutable sequence protocol (indexing, slicing, len, in).

Syntax

isinstance(obj, collections.abc.Sequence)

The classic trap: str is a Sequence, so this check will not separate a list of strings from a single string, and your function will happily iterate it character by character — screen strings out explicitly. Do not read it as "read-only" either: list is a Sequence too, because MutableSequence derives from it, and there is no ABC meaning "cannot be modified". For your own class only __getitem__ and __len__ are required; __contains__, __iter__, __reversed__, index and count arrive as mixins.

Examples

import collections.abc as abc
print(isinstance([1], abc.Sequence))   # → True
print(isinstance((1,), abc.Sequence))   # → True
print(isinstance('hello', abc.Sequence), isinstance(range(3), abc.Sequence))   # → True True
print(isinstance({1, 2}, abc.Sequence), isinstance({'a': 1}, abc.Sequence))   # → False False
print(isinstance(iter([1, 2]), abc.Sequence))   # → False
print(issubclass(list, abc.MutableSequence), issubclass(tuple, abc.MutableSequence))   # → True False

See also

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