delegation_pattern.py

"""
Reference: https://en.wikipedia.org/wiki/Delegation_pattern
Author: https://github.com/IuryAlves

*TL;DR
Allows object composition to achieve the same code reuse as inheritance.
"""

from __future__ import annotations

from typing import Any, Callable, Union


class Delegator:
 """
 >>> delegator = Delegator(Delegate())
 >>> delegator.p1
 123
 >>> delegator.p2
 Traceback (most recent call last):
 ...
 AttributeError: 'Delegate' object has no attribute 'p2'
 >>> delegator.do_something("nothing")
 'Doing nothing'
 >>> delegator.do_anything()
 Traceback (most recent call last):
 ...
 AttributeError: 'Delegate' object has no attribute 'do_anything'
 """

 def __init__(self, delegate: Delegate):
 self.delegate = delegate

 def __getattr__(self, name: str) -> Union[Any, Callable]:
 attr = getattr(self.delegate, name)

 if not callable(attr):
 return attr

 def wrapper(*args, **kwargs):
 return attr(*args, **kwargs)

 return wrapper


class Delegate:
 def __init__(self):
 self.p1 = 123

 def do_something(self, something: str) -> str:
 return f"Doing {something}"


if __name__ == "__main__":
 import doctest

 doctest.testmod()