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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_transition(self, source: str, dest: str):
 """ Adds a transition from one state to another. Args: source (str):
 the name of the state from where the transition starts dest (str):
 the name of the state where the transition ends """

        self._transitions[source].append(dest)