Посредник

from abc import ABC, abstractmethod

class Mediator(ABC):
    @abstractmethod
    def send_message(self, message, sender):
        pass

class ChatMediator(Mediator):
    def __init__(self):
        self._users = []

    def add_user(self, user):
        self._users.append(user)

    def send_message(self, message, sender):
        for user in self._users:
            # Отправляем сообщение всем пользователям, кроме отправителя
            if user != sender:
                user.receive(message)

class User:
    def __init__(self, name, mediator):
        self.name = name
        self._mediator = mediator
        self._mediator.add_user(self)

    def send(self, message):
        print(f"{self.name} sends: {message}")
        self._mediator.send_message(message, self)

    def receive(self, message):
        print(f"{self.name} receives: {message}")

def main():
    mediator = ChatMediator()

    user1 = User("Alice", mediator)
    user2 = User("Bob", mediator)
    user3 = User("Charlie", mediator)

    user1.send("Hello, everyone!")
    user2.send("Hi, Alice!")
    user3.send("Hey, folks!")

main()

Alice sends: Hello, everyone!
Bob receives: Hello, everyone!
Charlie receives: Hello, everyone!
Bob sends: Hi, Alice!
Alice receives: Hi, Alice!
Charlie receives: Hi, Alice!
Charlie sends: Hey, folks!
Alice receives: Hey, folks!
Bob receives: Hey, folks!