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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_step(self, step, step_id):
 """ Add a step to the list. The first step added becomes the initial step. """

        assert step_id not in self._steps
        assert step_id not in self._order
        assert isinstance(step, Step)

        self._steps[step_id] = step
        self._order.append(step_id)