New submission from Sam Franklin :
When argparse wraps the usage text, it can fail its assertion tests with
whitespace differences. This can occur when metavar="", needed if a user wishes
to avoid having a metavar print. It also could occur if a user specifies any
other whitespace.
Here's a minimum example (depending on $COLUMNS):
import argparse
# based on Vajrasky Kok's script in https://bugs.python.org/issue11874
parser = argparse.ArgumentParser(prog='PROG')
parser.add_argument('--nil', metavar='', required=True)
parser.add_argument('--a', metavar='a' * 165)
parser.parse_args()
This produces the AssertionError at the bottom of this comment.
A solution is to have the two asserts ignore whitespace. I'll submit a pull
request very shortly for this. (First time so happy for any comments or
critiques!)
A more extensive example:
import argparse
# based on Vajrasky Kok's script in https://bugs.python.org/issue11874
parser = argparse.ArgumentParser(prog='PROG')
parser.add_argument('--nil', metavar='', required=True)
parser.add_argument('--Line-Feed', metavar='\n', required=True)
parser.add_argument('--Tab', metavar='\t', required=True)
parser.add_argument('--Carriage-Return', metavar='\r', required=True)
parser.add_argument('--Carriage-Return-and-Line-Feed',
metavar='\r\n', required=True)
parser.add_argument('--vLine-Tabulation', metavar='\v', required=True)
parser.add_argument('--x0bLine-Tabulation', metavar='\x0b', required=True)
parser.add_argument('--fForm-Feed', metavar='\f', required=True)
parser.add_argument('--x0cForm-Feed', metavar='\x0c', required=True)
parser.add_argument('--File-Separator', metavar='\x1c', required=True)
parser.add_argument('--Group-Separator', metavar='\x1d', required=True)
parser.add_argument('--Record-Separator', metavar='\x1e', required=True)
parser.add_argument('--C1-Control-Code', metavar='\x85', required=True)
parser.add_argument('--Line-Separator', metavar='\u2028', required=True)
parser.add_argument('--Paragraph-Separator', metavar='\u2029', required=True)
parser.add_argument('--a', metavar='a' * 165)
parser.parse_args()
This is related to https://bugs.python.org/issue17890 and
https://bugs.python.org/issue32867.
File "/minimum_argparse_bug.py", line 7, in
parser.parse_args()
File "/path/to/cpython/Lib/argparse.py", line 1758, in parse_args
args, argv = self.parse_known_args(args, namespace)
File "/path/to/cpython/Lib/argparse.py", line 1790, in parse_known_args
namespace, args = self._parse_known_args(args, namespace)
File "/path/to/cpython/Lib/argparse.py", line 1996, in _parse_known_args
start_index = consume_optional(start_index)
File "/path/to/cpython/Lib/argparse.py", line 1936, in consume_optional
take_action(action, args, option_string)
File "/path/to/cpython/Lib/argparse.py", line 1864, in take_action
action(self, namespace, argument_values, option_string)
File "/path/to/cpython/Lib/argparse.py", line 1037, in __call__
parser.print_help()
File "/path/to/cpython/Lib/argparse.py", line 2483, in print_help
self._print_message(self.format_help(), file)
File "/path/to/cpython/Lib/argparse.py", line 2467, in format_help
return formatter.format_help()
File "/path/to/cpython/Lib/argparse.py", line 281, in format_help
help = self._root_section.format_help()
File "/path/to/cpython/Lib/argparse.py", line 212, in format_help
item_help = join([func(*args) for func, args in self.items])
File "/path/to/cpython/Lib/argparse.py", line 212, in
item_help = join([func(*args) for func, args in self.items])
File "/path/to/cpython/Lib/argparse.py", line 336, in _format_usage
assert ' '.join(opt_parts) == opt_usage
AssertionError
--
components: Library (Lib)
messages: 350117
nosy: sjfranklin
priority: normal
severity: normal
status: open
title: argparse wrapping fails with metavar="" (no metavar)
type: crash
versions: Python 2.7, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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