Python argparse:它必须返回一个列表吗? [英] Python argparse: Does it have to return a list?

问题描述

我正在尝试从 argparse 获取一串数字.是否提供参数 -n 是可选的.

I am trying to obtain a string of numbers from argparse. It's optional whether or not the argument -n is provided.

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-n', nargs=1) # -n is optional but must come with one and only one argument
args = parser.parse_args()
test = args.n
if test != 'None':
    print("hi " + test) 

当我不提供-n 参数"时程序会失败，但是当我提供时它运行良好.

The program fails when I do not provide "-n argument", but works fine when I do.

Traceback (most recent call last):
  File "parse_args_test.py", line 7, in <module>
    print("hi " + test) 
TypeError: Can't convert 'NoneType' object to str implicitly

我该如何解决这个问题?

How can I fix this?

推荐答案

不要尝试连接 None 和 "hi ":

Do not try to concatenate None and "hi ":

print("hi", test)

或

print("hi " + (test or ''))

或测试 test 是否显式设置为 None:

or test if test is set to None explicitly:

if test is not None:
    print("hi", test)

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