Python argparse:是否必须返回列表? [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，程序将失败，但是当我提供时，它将运行正常.

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?

推荐答案

请勿尝试将None和"hi "连接起来:

Do not try to concatenate None and "hi ":

print("hi", test)

或

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

或测试是否将test显式设置为无":

or test if test is set to None explicitly:

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

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