Build state assignment code.

        @param state_assignment: State assignment object
        @type state_assignment: lems.model.dynamics.StateAssignment

        @return: Generated state assignment code
        @rtype: string

def build_state_assignment(self, runnable, regime, state_assignment):
        """
        Build state assignment code.

        @param state_assignment: State assignment object
        @type state_assignment: lems.model.dynamics.StateAssignment

        @return: Generated state assignment code
        @rtype: string
        """

        return ['self.{0} = {1}'.format(\
            state_assignment.variable,
            self.build_expression_from_tree(runnable,
                                            regime,
                                            state_assignment.expression_tree))]