AssertionError: assert ' '.join(pos_parts) == pos_usage

[petriborg]

Argparse 1.1 or 1.4 fails with AssertionError - the weird regex that reads the metavar value seems to blow up argparse.

#!/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())

$ ./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

[ThomasWaldmann]

Are you using python3.5? It has argparse builtin (in stdlib), so you do not need this package, it is only for python 2.6 users.

Bug reports for argparse in the stdlib should go into the python issue tracker.

[petriborg]

So is this repo just a backport of whatever is in stdlib? Since this was labeled 1.4 I was hoping it was a newer version that might have already fixed the bug I ran into.

Apparently it is this issue (with yet to be applied patch) for 2.7, 3.4, and 3.5.

I got some helpful hacks from Stackoverflow that might help others work around the bug.

[ThomasWaldmann]

It was backported some time ago from a version in stdlib and since then has independent versioning.