python argparser用于部分选择的多个参数 [英] python argparser for multiple arguments for partial choices

问题描述

我创建一个像这样的argparser:

I create a argparser like this:

  parser = argparse.ArgumentParser(description='someDesc')
  parser.add_argument(-a,required=true,choices=[x,y,z])
  parser.add_argument( ... )

但是，仅对于选项"x"而不是对于选项"y，z"，我想要一个附加的REQUIRED参数.例如.

However, only for choice "x" and not for choices "y,z", I want to have an additional REQUIRED argument. For eg.

python test -a x       // not fine...needs additional MANDATORY argument b
python test -a y       // fine...will run
python test -a z       // fine...will run  
python test -a x -b "ccc"       // fine...will run 

如何使用ArgumentParser完成此操作?我知道bash optparser可能实现

How can I accomplish that with ArgumentParser? I know its possible with bash optparser

推荐答案

详细解释子解析器方法:

To elaborate on the subparser approach:

sp = parser.add_subparsers(dest='a')
x = sp.add_parser('x')
y=sp.add_parser('y')
z=sp.add_parser('z')
x.add_argument('-b', required=True)

• 这与您的规范不同，因为不需要-a.
• dest='a'参数确保名称空间中有一个"a"属性.
• 通常不需要像'-b'这样的可选内容.子解析器"x"也可以采用所需的位置.
• this differs from your specification in that no -a is required.
• dest='a' argument ensures that there is an 'a' attribute in the namespace.
• normally an optional like '-b' is not required. Subparser 'x' could also take a required positional.

如果必须使用-a可选选项，则可以进行两步解析

If you must use a -a optional, a two step parsing might work

p1 = argparse.ArgumentParser()
p1.add_argument('-a',choices=['x','y','z'])
p2 = argparse.ArgumentParser()
p2.add_argument('-b',required=True)
ns, rest = p1.parse_known_args()
if ns.a == 'x':
    p2.parse_args(rest, ns)

第三种方法是在事实发生后进行自己的测试.您仍然可以使用argparse错误机制

A third approach is to do your own test after the fact. You could still use the argparse error mechanism

parser.error('-b required with -a x')

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