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

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