Callback experiment (async alternative)

defer.py

from concurrent.futures import ThreadPoolExecutor

_pool = ThreadPoolExecutor()

def defer(caller, *args, **kwargs):
    def decorator(func):
        global _pool
        future = _pool.submit(caller, *args, **kwargs)
        future.add_done_callback(lambda f: func(f.result()))
        return func
    return decorator


if __name__ == "__main__":
    import time

    def concat(a, b):
        time.sleep(0.3)
        return a + b


    def main():
        prefix = "pre_"
        suffix = "suff"

        @defer(concat, prefix, suffix)
        def _(value):
            print("after execution", value)

            @defer(concat, "more_", value)
            def _(value):
                print("more after", value)

        print("before execution")

    main()
    time.sleep(0.8)