code: def add_assignment_clause(self, clause):
          
          if not isinstance(clause, AssignmentClause):
              raise StatementException("only instances of AssignmentClause can be added to statements")
          clause.set_context_id(self.context_counter)
          self.context_counter += clause.get_context_size()
          self.assignments.append(clause)
docs: adds an assignment clause to this statement
          :param clause: the clause to add
          :type clause: AssignmentClause