after()

Create a function that only invokes the provided function after it has been called a specified number of times.

Implementation

Accepts (func, n) or (n, func). The wrapped function will only execute the original `func` on the nth and subsequent calls; before that, it returns None. Parameters: a : Callable[..., R] or int The function to wrap or the number of calls to wait before invoking. b : int or Callable[..., R] The number of calls to wait before invoking or the function to wrap. Returns: A wrapped function that executes `func` only after the specified number of invocations.

Example

                            def greet():
    return "Hello!"
greet_after_3 = after(greet, 3)
greet_after_3()  # None
greet_after_3()  # None
greet_after_3()  # "Hello!"
                        

Expected output: Function that prints only after being called 3 times

Source Code

                        def after(a: Any, b: Any) -> Callable[..., Optional[R]]:

    if callable(a) and isinstance(b, int):
        func, times = a, b
    elif isinstance(a, int) and callable(b):
        times, func = a, b  # swapped
    else:
        raise TypeError("after expects (func, int) or (int, func)")

    count = [0]
    def wrapper(*args: Any, **kwargs: Any) -> Optional[R]:
        count[0] += 1
        if count[0] >= max(times, 1):
            return func(*args, **kwargs) # type: ignore
        return None

    wrapper.__name__    = func.__name__
    wrapper.__doc__     = func.__doc__
    wrapper.__wrapped__ = func # type: ignore
    return wrapper
                    