来自metavar`[[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失败，并显示AssertionError-读取metavar值的怪异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 AssertionError ?

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?

是否有其他替代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())

Shell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，并使用清理后的值进行后处理.这样做的一种方法可能是这样的:

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器构造解析器

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,
    )

将其余的放入所提供的代码中，将产生类似这样的结果

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

自然，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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