Type annotations for *args and **kwargs
The proper way to do this is using @overload
from typing import overload
@overload
def foo(arg1: int, arg2: int) -> int:
...
@overload
def foo(arg: int) -> int:
...
def foo(*args):
try:
i, j = args
return i + j
except ValueError:
assert len(args) == 1
i = args[0]
return i
print(foo(1))
print(foo(1, 2))
Note that you do not add @overload
or type annotations to the actual implementation, which must come last.
You'll need a newish version of both typing
and mypy to get support for @overload outside of stub files.
You can also use this to vary the returned result in a way that makes explicit which argument types correspond with which return type. e.g.:
from typing import Tuple, overload
@overload
def foo(arg1: int, arg2: int) -> Tuple[int, int]:
...
@overload
def foo(arg: int) -> int:
...
def foo(*args):
try:
i, j = args
return j, i
except ValueError:
assert len(args) == 1
i = args[0]
return i
print(foo(1))
print(foo(1, 2))
For variable positional arguments (*args
) and variable keyword arguments (**kw
) you only need to specify the expected value for one such argument.
From the Arbitrary argument lists and default argument values section of the Type Hints PEP:
Arbitrary argument lists can as well be type annotated, so that the definition:
def foo(*args: str, **kwds: int): ...
is acceptable and it means that, e.g., all of the following represent function calls with valid types of arguments:
foo('a', 'b', 'c') foo(x=1, y=2) foo('', z=0)
So you'd want to specify your method like this:
def foo(*args: int):
However, if your function can only accept either one or two integer values, you should not use *args
at all, use one explicit positional argument and a second keyword argument:
def foo(first: int, second: Optional[int] = None):
Now your function is actually limited to one or two arguments, and both must be integers if specified. *args
always means 0 or more, and can't be limited by type hints to a more specific range.