在Python中，使用argparse，仅允许使用正整数 [英] In Python, using argparse, allow only positive integers

问题描述

标题几乎总结了我想发生的事情.

The title pretty much summarizes what I'd like to have happen.

这里是我所拥有的，虽然程序不会在非正整数上崩溃，但我希望通知用户非正整数基本上是无意义的.

Here is what I have, and while the program doesn't blow up on a nonpositive integer, I want the user to be informed that a nonpositive integer is basically nonsense.

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-g", "--games", type=int, default=162,
                    help="The number of games to simulate")
args = parser.parse_args()

输出:

python simulate_many.py -g 20
Setting up...
Playing games...
....................

输出为负:

python simulate_many.py -g -2
Setting up...
Playing games...

现在，显然我可以添加一个if来确定if args.games是否为负，但是我很好奇是否有一种方法可以将其捕获在argparse级别，以便利用自动用法打印.

Now, obviously I could just add an if to determine if args.games is negative, but I was curious if there was a way to trap it at the argparse level, so as to take advantage of the automatic usage printing.

理想情况下，它将打印类似以下内容的内容:

Ideally, it would print something similar to this:

python simulate_many.py -g a
usage: simulate_many.py [-h] [-g GAMES] [-d] [-l LEAGUE]
simulate_many.py: error: argument -g/--games: invalid int value: 'a'

像这样:

python simulate_many.py -g -2
usage: simulate_many.py [-h] [-g GAMES] [-d] [-l LEAGUE]
simulate_many.py: error: argument -g/--games: invalid positive int value: '-2'

现在我正在这样做，我想我很高兴:

For now I'm doing this, and I guess I'm happy:

if args.games <= 0:
    parser.print_help()
    print "-g/--games: must be positive."
    sys.exit(1)

推荐答案

使用type应该可以实现.您仍然需要定义一个实际的方法来为您决定:

This should be possible utilizing type. You'll still need to define an actual method that decides this for you:

def check_positive(value):
    ivalue = int(value)
    if ivalue <= 0:
        raise argparse.ArgumentTypeError("%s is an invalid positive int value" % value)
    return ivalue

parser = argparse.ArgumentParser(...)
parser.add_argument('foo', type=check_positive)

这基本上只是 docs 中perfect_square函数的改编示例argparse上的a>.

This is basically just an adapted example from the perfect_square function in the docs on argparse.

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