为什么 Python 将列表匹配为元组？

Question

With Python 3.11.0a2+, and the following code:

def my_fun(e):
    match e:
        case (1,):
            print("tuple (1,)")
        case [1]:
            print("list [1]")
        case _:
            print("I don't understand")

Calling the function with my_fun([1]) prints "tuple (1,)".

Is this behavior correct?

If I explicitly match against tuple((1, )) instead of (1,) , it works as expected.

If this is not a bug of the interpreter, what is the reason behind this seemingly weird behavior?

Answer 1

This isdocumented under Structural Pattern Matching .

Like unpacking assignments, tuple and list patterns have exactly the same meaning and actually match arbitrary sequences . Technically, the subject must be a sequence. Therefore, an important exception is that patterns don't match iterators. Also, to prevent a common mistake, sequence patterns don't match strings.

and in PEP 635 -- Structural Pattern Matching: Motivation and Rationale

As in iterable unpacking, we do not distinguish between ' tuple ' and ' list ' notation. [a, b, c] , (a, b, c) and a, b, c are all equivalent. While this means we have a redundant notation and checking specifically for lists or tuples requires more effort (eg case list([a, b, c])) , we mimic iterable unpacking as much as possible.