来自元变量`[[USER@]HOST:]FILE`的Python argparse AssertionError [英] Python argparse AssertionError from metavar `[[USER@]HOST:]FILE`

问题描述

Argparse 1.1 或 1.4 因 AssertionError 失败 - 读取元变量值的奇怪正则表达式似乎炸毁了 argparse - 可能与 当参数数量超过阈值时，Python argparse 断言错误?

Argparse 1.1 or 1.4 fails with AssertionError - the weird regex that reads the metavar value seems to blow up argparse - Possibly related to Python argparse AssertionError when number of arguments exceeds threshold?

是否有其他方法可以创建或使用元变量 [[USER@]HOST:]FILE?

Is there any alternative way to create or use the metavar [[USER@]HOST:]FILE?

测试设置:

$ virtualenv-3.5 --always-copy test2
$ ./test2/bin/pip install argparse

Python 代码 test.py:

Python code test.py:

#!/Users/[username]/Development/test2/bin/python3.5

import os
import sys
print('sys.prefix', sys.prefix)
sys.path.insert(
    0, os.path.join(sys.prefix, 'lib/python3.5/site-packages'))

import argparse
print('argparse', argparse.__version__)

parser = argparse.ArgumentParser()
parser.add_argument(
    'files',
    metavar='[[USER@]HOST:]FILE',
    nargs=argparse.PARSER,
    )
parser.add_argument('-a', '-A', metavar='PTRN', dest='patterns', default=[])
parser.add_argument('-b', '-B', metavar='PTRN', dest='patterns', default=[])
parser.add_argument('-c', '-C', metavar='PTRN', dest='patterns', default=[])
parser.add_argument('-d', '-D', metavar='PTRN', dest='patterns', default=[])
parser.add_argument('-e', '-E', metavar='PTRN', dest='patterns', default=[])
parser.add_argument('-f', '-F', metavar='PTRN', dest='patterns', default=[])
print(parser.parse_args())

外壳输出:

$ ./test.py
sys.prefix /Users/[username]/Development/test2/bin/..
argparse 1.4.0
Traceback (most recent call last):
  File "./test.py", line 24, in <module>
    print(parser.parse_args())
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 1725, in parse_args
    args, argv = self.parse_known_args(args, namespace)
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 1754, in parse_known_args
    namespace, args = self._parse_known_args(args, namespace)
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 1971, in _parse_known_args
    self.error(_('too few arguments'))
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 2391, in error
    self.print_usage(_sys.stderr)
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 2353, in print_usage
    self._print_message(self.format_usage(), file)
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 2309, in format_usage
    return formatter.format_help()
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 306, in format_help
    help = self._root_section.format_help()
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 236, in format_help
    func(*args)
  File "/Users/[username]/Development/test2/bin/../lib/python3.5/site-packages/argparse.py", line 358, in _format_usage
    assert ' '.join(pos_parts) == pos_usage
AssertionError

推荐答案

解决方法是创建自定义帮助格式化程序并使用经过处理的值进行后处理.一种方法可以是这样:

The workaround is to create a custom help formatter and do post-processing using a sanitized value. One way to do so can be like so:

class MyHelpFormatter(argparse.HelpFormatter):

    def _format_usage(self, usage, actions, groups, prefix):
        result = super(MyHelpFormatter, self)._format_usage(
            usage, actions, groups, prefix)
        return result.format(user_host_file='[[USER@]HOST]:FILE')

然后使用自定义格式化程序构建解析器

Then construct the parser using the custom formattter

parser = argparse.ArgumentParser(formatter_class=MyHelpFormatter)
parser.add_argument(
    'files',
    metavar='{user_host_file}',
    nargs=argparse.PARSER,
    )

将其余部分插入提供的代码中，就产生了这样的东西

Plugging the rest into the code supplied, something like this is produced

$ python demo.py 
('argparse', '1.1')
usage: demo.py [-h] [-a PTRN] [-b PTRN] [-c PTRN] [-d PTRN] [-e PTRN]
               [-f PTRN]
               [[USER@]HOST]:FILE ...
demo.py: error: too few arguments

当然，确切的策略可以像在格式化程序中使用 str.replace 方法一样简单，也可以比 str.format 方法更复杂.

Naturally, the exact strategy can be as simple as using the str.replace method in the formatter, or more complicated than the str.format method.

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