<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_step_visible(self, step):
 """ Returns whether the given `step` should be included in the wizard; it is included if either the form is idempotent or not filled in before. """

        return self.idempotent_dict.get(step, True) or \
            step not in self.storage.validated_step_data