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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 add(self, msg, callback, override=False):
 """Add a callback to the callback list. msg: Message template. callback: Callback method override: True - replace all existing callbacks for that template False - append the list of callbacks for that message Default is False """

        if override:
            if isinstance(callback, list):
                self._dict[msg] = callback
            else:
                self._dict[msg] = [callback]
        else:
            cb = self[msg]
            cb.append(callback)
            self._dict[msg] = cb