timer.py

import functools
import datetime
 
def with_time(func):     
    @functools.wraps(func)
    def timed_execution(*args, **kwargs):
        start = datetime.datetime.now()
        try:
            result = func(*args, **kwargs)
            time = datetime.datetime.now() - start
            return time, result
        except Exception as e:
            return None, e
            
    return timed_execution
 
class InvalidResult(Exception):
    pass
 
def valid_with_time(validator=None):
    def decorator(func):
        timed_execution = with_time(func)
        @functools.wraps(func)
        def valid_execution(*args, **kwargs):          
            time, result = timed_execution(*args, **kwargs)
            try:
                if time is not None:
                    validator(result)
                return time, result
            except InvalidResult as e:
                return None, e
        return valid_execution
    return decorator
 
@with_time
def add_five(n):
    return n + 5
 
def check_small(x):
    if x > 100: 
      raise InvalidResult("Number too large")
 
@valid_with_time(validator=check_small)
def add_numbers(a, b):
    return a + b
 
print add_five(37)
print add_numbers(20, 40)
print add_numbers(100, 1)