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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 combinations(self):
 """Returns a generator of all possible combinations. """

        keys = self._vars.keys()
        for result in product(*self._vars.values()):
            possible_solution = {}
            for i, v in enumerate(result):
                possible_solution[keys[i]] = v
            yield possible_solution