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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def subscribe(object_type: str, subscriber: str, callback_handler: Callable = None) -> EventQueue: """Subscribe to the specified object type. Returns an EventQueue object which can be used to query events associated with the object type for this subscriber. Args: object_type (str):
 Object type subscriber (str):
 Subscriber name callback_handler (function, optional):
 Callback handler function. Returns: EventQueue, event queue object. """

    key = _keys.subscribers(object_type)
    DB.remove_from_list(key, subscriber)
    DB.append_to_list(key, subscriber)
    return EventQueue(object_type, subscriber, callback_handler)