本文介绍了带有可检测开关的python argparse可选位置参数的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我想调用program -s <optional value>这样的程序.我想分配一个默认值,但也希望能够检测是否给出了-s开关.我所拥有的:

I would like to invoce my programm like program -s <optional value>. I would like to assign a default value, but would also like to be able to detect if the -s switch was given.What I have:

max_entries_shown = 10
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-s",
    nargs = '?',
    default = max_entries_shown)
args = parser.parse_args()

如果我没有在命令行上给出-s,那么给我args.s的值是10,如果我没有指定值的-s则给None.如果没有开关,我想要的是args.s等于None,并且在给定-s的情况下将args.s设置为默认值,如果以program -s custom_value运行,则args.s等于custom_value.我该如何实现?

This gives me a value of 10 for args.s if I don't give -s on the command line, and None if I specify -s without a value. What I want is args.s equal to None if no switch is given, and args.s set to the default value with -s given, and args.s equal to custom_value if run as program -s custom_value. How can I achive this?

推荐答案

您必须使用const而不是default.引用argparse Python Docs中有关何时使用 const 的提示:

You have to use const instead of default. Quote from argparse Python Docs about when to use const:

此外,我添加了type=int,因为我假设您想将输入视为整数.

Additionally, I added a type=int because I assumed that you want to treat the input as an int.

因此,您的代码应为:

max_entries_shown = 10
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-s",
    nargs = '?',
    const = max_entries_shown,
    type=int)
args = parser.parse_args()

此代码返回(带有打印参数)

This code returns (with print args)

$ python parse.py
Namespace(s=None)
$ python parse.py -s
Namespace(s=10)
$ python parse.py -s 12
Namespace(s=12)

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08-22 19:46
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