How to Use Elypsis in Type Hints to Indicate Arbitrary Number of Elements

In type hints, ... (ellipsis) is used to indicate that a function parameter or return value can have an arbitrary number of arguments or elements.

For example, if you have a function that takes an arbitrary number of integers as arguments, you can use ... in the function signature to indicate that:

def foo(*args: int) -> List[int]:
    return [x * 2 for x in args]

Here, *args is used to indicate that the function can take any number of arguments, and the int type hint indicates that each argument must be an integer. The return type is a list of integers.

Similarly, you can use ... in a type hint for a tuple to indicate that the tuple can have an arbitrary number of elements of a given type. For example:

from typing import Tuple

def bar(t: Tuple[str, ...]) -> str:
    return " ".join(t)

t1 = ("hello", "world")
t2 = ("foo", "bar", "baz")

print(bar(t1))  # Output: "hello world"
print(bar(t2))  # Output: "foo bar baz"

Here, Tuple[str, ...] is used to indicate that t is a tuple of strings, and the ... indicates that the tuple can have an arbitrary number of elements.

X::Python - How to Make Type Hint for the Tuple With Undetermined Number of Strings?

X::Use Python TypedDict to Type Hint Dictionaries