Function decorator that accepts optional keyword-argument

decorator wraps overload

Source

• self, with help from GitHub Copilot
• inspired by @dataclass’s handling of optional keyword arguments (albeit being to decorate classes rather than functions)

from __future__ import annotations
 
from functools import wraps
from typing import overload
 
 
@overload
def func_decorator_with_and_without_args(func): ...
 
 
@overload
def func_decorator_with_and_without_args(*, dkwarg="default_kwarg"): ...
 
 
def func_decorator_with_and_without_args(*dargs, dkwarg="default_kwarg"):
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            print(
                f"func_decorator_with_and_without_args: Calling {func.__name__} with args: {args}, kwargs: {kwargs}, "
                f"decorator dkwarg: {dkwarg}"
            )
            return func(*args, **kwargs)
 
        return wrapper
 
    print(f"decorator dargs: {dargs}, decorator dkwarg: {dkwarg}")
 
    if len(dargs) > 1:
        raise ValueError("Only one positional argument is allowed (the function to decorate)")
 
    # see if we're being called as @decorator or @decorator()
    if len(dargs) == 0:
        # we're called with parentheses as @decorator(kwargs...)
        return decorator
 
    # we're called as @decorator without parentheses
    func = dargs[0]
    if not callable(func):
        raise TypeError("The function to decorate must be a callable")
    return decorator(func)
 
# valid usage -----------------------------------------------------------
 
@func_decorator_with_and_without_args
def func(*args, **kwargs):
    print(f"func args: {args}, kwargs: {kwargs}")
 
@func_decorator_with_and_without_args(dkwarg="dkwarg")
def func_with_args(*args, **kwargs):
    print(f"func_with_args args: {args}, kwargs: {kwargs}")
 
# invalid usage ---------------------------------------------------------
 
@func_decorator_with_and_without_args()
def func_with_empty_parens(*args, **kwargs):
    print(f"func_with_empty_parens args: {args}, kwargs: {kwargs}")
 
@func_decorator_with_and_without_args("darg")
def func_with_single_arg_invalid(*args, **kwargs):
    print(f"func_with_single_arg_invalid args: {args}, kwargs: {kwargs}")
 
@func_decorator_with_and_without_args("darg1", "darg2")
def func_with_args_invalid(*args, **kwargs):
    print(f"func_with_args_invalid args: {args}, kwargs: {kwargs}")
 
@func_decorator_with_and_without_args(dkwarg="dkwarg", dkwarg2="dkwarg2")
def func_with_multiple_kwargs_invalid(*args, **kwargs):
    print(f"func_with_multiple_kwargs_invalid args: {args}, kwargs: {kwargs}")