How to short-circuit a function using Python decorators?

Question

Say I have a function F that may return boolean false. If I have a caller named main() that will call F in multiple places, can I attach a decorator to F that will propagate the return value and cause its parent (main) to also exit early?

Answer 1

No function can 'return' to a context higher than it's caller. This (to my knowledge) is universal in most programming languages. You could probably hack it by inspecting the python state and call stack, but a much better / more appropriate solution would be to wrap main in a try: except: block that catches a custom exception that you raise inside this decorator depending on the output of F()

import random
from functools import wraps

class ShortCircuit(Exception):
    pass

def short_circuit(f):
    @wraps(f)
    def wrapped(*args, **kwargs):
        res = f(*args, **kwargs)
        if not res:
            raise ShortCircuit()
        else:
            return res
    return wrapped

@short_circuit
def F():
    return random.choice([True, False])

def main():
    print(F())
    print(F())

if __name__=="__main__":
    try:
        main()
    except ShortCircuit:
        print("short circuited")