如何在 argparse 中使用可选参数？

如何解决如何在 argparse 中使用可选参数？

在以下源代码中，可选参数 txt 和 rtf 无法正常工作。

程序必须能够将 txt 或 rtf 作为参数，而不是两者。

from argparse import ArgumentParser


class MainClass:
    @classmethod
    def main(cls):
        print("[Start of Main]")

        # initialize argument parser
        my_parser = ArgumentParser()
        my_parser.add_argument("-i",help="input directory",type=str)
        my_parser.add_argument("-o",help="output directory",type=str)
        my_parser.add_argument("--txt",help="output as .txt files")
        my_parser.add_argument("--rtf",help="output as .rtf files")

        # parse the argument
        args = my_parser.parse_args()

        if args.i is None:
            print("INPUT: current directory")
        else:
            print("INPUT: specific directory " + args.i)

        if args.o is None:
            print("OUTPUT: current directory")
        else:
            print("OUTPUT: specific directory " + args.o)

        if args.txt is not None and args.rtf is not None:
            print("Default output is .txt")
        elif args.txt is None and args.rtf is None:
            print("Default output is .txt")
        elif args.txt is not None:
            print(".txt output")
        elif args.rtf is not None:
            print(".rtf output")


        print("[End of Main]")


if __name__ == '__main__':
    MainClass.main()

输出

C:\Users\pc\source\>python command_line_args_test.py -o "c:\\" --rtf
[Start of Main]
INPUT: current directory
OUTPUT: specific directory c:\ --rtf
Default output is .txt
[End of Main]

我该如何解决？