Concise example

events.py

class BaseEvent:
    def __init__(self, bot=None, conn=None, hook=None, base_event=None):
        self.bot = bot
        self.conn = conn
        self.hook = hook
        if base_event is not None:
            # We're copying an event, so inherit values
            if self.bot is None and base_event.bot is not None:
                self.bot = base_event.bot
            if self.conn is None and base_event.conn is not None:
                self.conn = base_event.conn
            if self.hook is None and base_event.hook is not None:
                self.hook = base_event.hook