code: def p_string_list(self, p):
          '''string_list : string_list COMMA IDENT
                         | IDENT
                         | empty'''
          if p[1] is None:
              p[0] = []
          elif len(p) == 4:
              p[1].append(p[3])
              p[0] = p[1]
          elif len(p) == 2:
              p[0] = [p[1]f p_string_list(self, p):
          '''string_list : string_list COMMA IDENT
                         | IDENT
                         | empty'''
          if p[1] is None:
              p[0] = []
          elif len(p) == 4:
              p[1].append(p[3])
              p[0] = p[1]
          elif len(p) == 2:
              p[0] = [p[1]]
docs: string_list : string_list COMMA IDENT
                         | IDENT
                         | empty