Python 参数解析 : list individual choices in the usage

Question

我有一个接受多个参数的程序，例如

breakfast.py --customer=vikings eggs sausage bacon

可以从特定选项列表中指定“鸡蛋”、“香肠”和“培根”。

现在我希望 breakfast.py --help 的输出看起来像这样:

usage: breakfast.py [-h] [--customer CUSTOMER] INGREDIENT [INGREDIENT ...]

positional arguments:
  your choice of ingredients:
    bacon              Lovely bacon
    egg                The runny kind
    sausage            Just a roll
    spam               Glorious SPAM
    tomato             Sliced and diced

optional arguments:
  -h, --help           show this help message and exit
  --customer CUSTOMER  salutation for addressing the customer

我尝试了两种方法，但到目前为止都失败了。

使用参数选择:

import argparse

parser = argparse.ArgumentParser()

toppings = {
    'bacon': "Lovely bacon",
    'egg': 'The runny kind',
    'sausage': 'Just a roll',
    'spam': 'Glorious SPAM',
    'tomato': 'Sliced and diced',
}
parser.add_argument('--customer', default='Mr. and Mrs. Bun', action='store',
                    help='salutation for addressing the customer')
parser.add_argument('ingredients', nargs='+', choices=toppings.keys(),
                    help='your choice of ingredients')

options = parser.parse_args('--customer=Vikings egg sausage bacon'.split())
print("Dear {}, we are happy to serve you {}" \
      .format(options.customer, ', '.join(options.ingredients)))

上述程序的用法是打印一个没有详细信息的字典格式的列表:

usage: breakfast.py [-h] [--customer CUSTOMER]
                      {bacon,egg,sausage,spam,tomato}
                      [{bacon,egg,sausage,spam,tomato} ...]

positional arguments:
  {bacon,egg,sausage,spam,tomato}
                        your choice of ingredients

将 metavar='INGREDIENT' 添加到 add_argument('ingredients', ...) 根本不列出选项:

usage: breakfast.py [-h] [--customer CUSTOMER] INGREDIENT [INGREDIENT ...]

positional arguments:
  INGREDIENT           your choice of ingredients

我曾短暂地尝试过使用子程序:

import argparse

parser = argparse.ArgumentParser()

parser.add_argument('--customer', default='Mr. and Mrs. Bun', action='store',
                    help='salutation for addressing the customer')
ingredients = parser.add_subparsers(title='your choice of an ingredient',
                    dest='ingredient', metavar='ingredient')
ingredients.add_parser('bacon', help="Lovely bacon")
ingredients.add_parser('egg', help="The runny kind")
ingredients.add_parser('sausage', help="Just a roll")
ingredients.add_parser('spam', help="Glorious SPAM")
ingredients.add_parser('tomato', help="Sliced and diced")

options = parser.parse_args('--customer=Vikings spam'.split())
print("Dear {}, we are happy to serve you {}" \
      .format(options.customer, options.ingredient))

它以我喜欢的方式列出了用法:

usage: breakfast.py [-h] [--customer CUSTOMER] ingredient ...

optional arguments:
  -h, --help           show this help message and exit
  --customer CUSTOMER  salutation for addressing the customer

your choice of an ingredient:
  ingredient
    bacon              Lovely bacon
    egg                The runny kind
    sausage            Just a roll
    spam               Glorious SPAM
    tomato             Sliced and diced

默认情况下，子程序只允许选择一个选项。还好this answer shows it is possible to allow multiple subcommands )，但这感觉就像是为了获得正确的格式。我最近从 argparse 转移到 ConfigArgParse ，而这种方法在那里失败了。

我认为我最好恢复使用具有多个选项的单个参数，并使用自定义格式。

不幸的是，关于调整 argparse 格式的文档很少，所以我很感激一些帮助如何解决这个问题。

Answer 1

将 add_argument 更改为:

parser.add_argument('ingredients', nargs='+', choices=toppings.keys(),
                metavar='INGREDIENT',
                help='your choice of ingredients: %(choices)s')

产生

usage: stack49969605.py [-h] [--customer CUSTOMER] INGREDIENT [INGREDIENT ...]

positional arguments:
  INGREDIENT           your choice of ingredients: bacon, egg, sausage, spam,
                       tomato

更改格式化程序:

formatter_class=argparse.RawTextHelpFormatter

和 add_argument help 参数:

                    help = """
your choice of ingredients:
bacon              Lovely bacon
egg                The runny kind
sausage            Just a roll
spam               Glorious SPAM
tomato             Sliced and diced
    """
    )

产生:

usage: stack49969605.py [-h] [--customer CUSTOMER] INGREDIENT [INGREDIENT ...]

positional arguments:
  INGREDIENT           
                       your choice of ingredients:
                       bacon              Lovely bacon
                       egg                The runny kind
                       sausage            Just a roll
                       spam               Glorious SPAM
                       tomato             Sliced and diced

或者您可以使用 argparse.RawDescriptionHelpFormatter，并将格式化的表格放在 description 或 epilog 中。

---

另一种选择是创建一个模仿 subparsers 类方面的 Action 子类。但这需要更深入地了解如何在格式中处理此 Action 类。

class _SubParsersAction(Action):
    class _ChoicesPseudoAction(Action):

subparsers Action 对象维护此 PseudoAction 类的 _choices_actions 列表，仅用于欺骗帮助格式化程序显示子解析器就好像它们是一组嵌套的 Actions。该列表不用于解析；仅用于帮助格式化。