list(StateVariable): List all of the state variables written

def all_state_variables_written(self):
        '''
            list(StateVariable): List all of the state variables written
        '''
        all_state_variables_written = [f.all_state_variables_written() for f in self.functions + self.modifiers]
        all_state_variables_written = [item for sublist in all_state_variables_written for item in sublist]
        return list(set(all_state_variables_written))