code: def p_expr_unary_op(p):
      '''expr : PLUS expr
              | MINUS expr
              | NOT expr
              | BOOLEAN_NOT expr'''
      p[0] = ast.UnaryOp(p[1], p[2], lineno=p.lineno(1)f p_expr_unary_op(p):
      '''expr : PLUS expr
              | MINUS expr
              | NOT expr
              | BOOLEAN_NOT expr'''
      p[0] = ast.UnaryOp(p[1], p[2], lineno=p.lineno(1))
docs: expr : PLUS expr
              | MINUS expr
              | NOT expr
              | BOOLEAN_NOT expr