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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 _invert_dictionary(self, d):
 """Invert a dictionary. """

        inv_dict = {}

        for k, v in d.items():
            inv_dict[v] = inv_dict.get(v, [])
            inv_dict[v] += [k]

        return inv_dict