argparse默认选项基于另一个选项 [英] argparse default option based on another option

问题描述

假设我有一个argparse python脚本:

Suppose I have an argparse python script:

import argparse
parser = argparse.ArgumentParser()

parser.add_argument("--foo", required=True)

现在，我想添加另一个选项--bar，它将默认为在--foo参数指定的内容后面附加"_BAR".

Now I want to add another option --bar, which would default to appending "_BAR" to whatever was specified by --foo argument.

我的目标:

>>> parser.parse_args(['--foo', 'FOO'])
>>> Namespace(foo='FOO', bar="FOO_BAR")

AND

>>> parser.parse_args(['--foo', 'FOO', '--bar', 'BAR'])
>>> Namespace(foo='FOO', bar="BAR")

我需要这样的东西:

parser.add_argument("--bar", default=get_optional_foo + "_BAR")

推荐答案

这是编写自定义Action类的另一种尝试

Here's another attempt at writing a custom Action class

import argparse
class FooAction(argparse.Action):
    # adapted from documentation
    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest, values)
        defaultbar = getattr(namespace, 'bar')
        try:
            defaultbar = defaultbar%values
        except TypeError:
            # BAR has already been replaced
            pass
        setattr(namespace, 'bar', defaultbar)

parser = argparse.ArgumentParser()
parser.add_argument("--foo", required=True, action=FooAction)
parser.add_argument("--bar", default="%s_BAR")

args = parser.parse_args(['--foo', 'Foo', '--bar', 'Bar'])
# Namespace(bar='Bar', foo='Foo')
args = parser.parse_args(['--foo', 'Foo'])
# Namespace(bar='Foo_BAR', foo='Foo')
args = parser.parse_args(['--bar', 'Bar', '--foo', 'Foo'])
# Namespace(bar='Bar', foo='Foo')

请注意，该类必须知道--bar参数的dest.另外，我使用'%s_BAR'可以轻松地区分默认值和非默认值.这样可以处理--bar出现在--foo之前的情况.

Note that the class has to know the dest of the --bar argument. Also I use a '%s_BAR' to readily distinguish between a default value, and a non default one. This handles the case where --bar appears before --foo.

使这种方法复杂化的是:

Things that complicate this approach are:

• 默认值在add_argument时间评估.
• 默认值放置在parse_args开头的命名空间中.
• 已标记(可选)的参数可以按任何顺序出现
• Action类不适用于处理交互参数.
• 在默认情况下，不会调用bar操作.
• bar默认值可以是一个函数，但是在parse_args之后必须检查是否需要对其进行评估.

• default values are evaluated at add_argument time.
• default values are placed in the Namespace at the start of parse_args.
• flagged (optionals) arguments can occur in any order
• the Action class is not designed to handle interacting arguments.
• the bar action will not be called in the default case.
• the bar default could be a function, but something would have to check after parse_args whether it needs to be evaluated or not.

尽管此自定义Action可以解决问题，但我仍然认为我的其他答案中的addbar函数是更干净的解决方案.

While this custom Action does the trick, I still think the addbar function in my other answer is a cleaner solution.

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