How to annotate function that takes a tuple of variable length in python?

问题

I have a function that takes a tuple of different lengths as an argument:

from typing import Tuple


def process_tuple(t: Tuple[str]):
    # Do nasty tuple stuff

process_tuple(("a",))
process_tuple(("a", "b"))
process_tuple(("a", "b", "c"))

When I annotate function like mentioned above, I get these error messages

fool.py:9: error: Argument 1 to "process_tuple" has incompatible type "Tuple[str, str]"; expected "Tuple[str]"
fool.py:10: error: Argument 1 to "process_tuple" has incompatible type "Tuple[str, str, str]"; expected "Tuple[str]"

process_tuple really works with tuples and I use them as immutable lists of variable length. I haven't found any consensus on this topic on the internet, so I wonder how should I annotate this kind of input.

回答1:

Variable length homogeneous tuple we can annotate using ... literal (aka Ellipsis) like

def process_tuple(t: Tuple[str, ...]):
    ...

after that errors should go away.

From docs

To specify a variable-length tuple of homogeneous type, use literal ellipsis, e.g. Tuple[int, ...]. A plain Tuple is equivalent to Tuple[Any, ...], and in turn to tuple.

回答2:

In addition to the Ellipsis answer as posted by Azat you could make it more explicit by using @typing.overload or typing.Union

from typing import Tuple


@overload
def process_tuple(t: Tuple[str]):
    # Do nasty tuple stuff

@overload
def process_tuple(t: Tuple[str, str]):
    ...

Or with the Union:

from typing import Tuple, Union


def process_tuple(t: Union[Tuple[str], Tuple[str, str], Tuple[str, str, str]]):
    # Do nasty tuple stuff

来源：https://stackoverflow.com/questions/54747253/how-to-annotate-function-that-takes-a-tuple-of-variable-length-in-python