python cast function output to specifc type. most commonly decorate generator to return a list.

as_list.py

def as_list(func: Callable[..., Iterator[T]]) -> Callable[..., list[T]]:
    """Decorator that casts the output of the function to a list.

    Example:
        >>> @as_list
        ... def foo():
        ...     yield 123
        ...
        >>> foo()
        [123]
    """

    @functools.wraps(func)
    def as_list_wrapper(*args, **kwargs):
        ret = func(*args, **kwargs)
        return list(ret)

    return as_list_wrapper

cast_to.py

import functools


def cast_to(cast_func):
    """Cast function's output to a specified type.

    Example:
        >>> @cast_to(list)
        ... def foo():
        ...     yield 123
        ...
        >>> foo()
        [123]
    """

    def decorator_cast_to(func):
        @functools.wraps(func)
        def wrapper_cast_to(*args, **kwargs):
            ret = func(*args, **kwargs)
            return cast_func(ret)

        return wrapper_cast_to

    return decorator_cast_to

timeit.py

In [7]: def a():
    l = []
    for i in range(10000):
        l.append("a{}".format(i))
    return l
   ...: 

In [8]: @cast_to(list)
def b():
    for i in range(10000):
        yield "a{}".format(i)
   ...:         

In [9]: %timeit a()
1.8 ms ± 25.9 µs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)

In [10]: %timeit b()
1.98 ms ± 16.6 µs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)