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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_activity_type(self, activity_type):
 """Adds an activity type to an Agent. Parameters activity_type : str The type of activity to add such as 'activity', 'kinase', 'gtpbound' """

        if activity_type not in self.activity_types:
            self.activity_types.append(activity_type)