能否告知python 2.7中的argparse至少需要两个参数? [英] Can argparse in python 2.7 be told to require a minimum of TWO arguments?

问题描述

我的应用程序是一种专用的文件比较实用程序，显然只比较一个文件没有意义，所以nargs='+'不太合适.

My application is a specialized file comparison utility and obviously it does not make sense to compare only one file, so nargs='+' is not quite appropriate.

nargs=N仅允许最多N个参数，但是只要有至少两个参数，我就需要接受无限数量的参数.

nargs=N only excepts a maximum of N arguments, but I need to accept an infinite number of arguments as long as there are at least two of them.

推荐答案

简短的答案是您不能这样做，因为nargs不支持"2+"之类的东西.

Short answer is you can't do that because nargs doesn't support something like '2+'.

长答案是您可以使用以下方法解决此问题:

Long answer is you can workaround that using something like this:

parser = argparse.ArgumentParser(usage='%(prog)s [-h] file file [file ...]')
parser.add_argument('file1', nargs=1, metavar='file')
parser.add_argument('file2', nargs='+', metavar='file', help=argparse.SUPPRESS)
namespace = parser.parse_args()
namespace.file = namespace.file1 + namespace.file2

您需要的技巧是:

• 使用usage为解析器提供您自己的用法字符串
• 使用metavar在帮助字符串中显示具有不同名称的参数
• 使用SUPPRESS避免显示其中一个变量的帮助
• 合并两个不同的变量，只是向解析器返回的Namespace对象添加新属性

• Use usage to provide you own usage string to the parser
• Use metavar to display an argument with a different name in the help string
• Use SUPPRESS to avoid displaying help for one of the variables
• Merge two different variables just adding a new attribute to the Namespace object that the parser returns

上面的示例产生以下帮助字符串:

The example above produces the following help string:

usage: test.py [-h] file file [file ...]

positional arguments:
  file

optional arguments:
  -h, --help  show this help message and exit

，并且在传递少于两个参数时仍然会失败:

and will still fail when less than two arguments are passed:

$ python test.py arg
usage: test.py [-h] file file [file ...]
test.py: error: too few arguments

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