paul j3 <ajipa...@gmail.com> added the comment:
prefix_chars is a parameter of the parent _ActionsContainer
class _ActionsContainer(object):
def __init__(self,
description,
prefix_chars,
argument_default,
conflict_handler):
super(_ActionsContainer, self).__init__()
self.description = description
self.argument_default = argument_default
self.prefix_chars = prefix_chars
self.conflict_handler = conflict_handler
add_argument is also a method in this class. It uses its own prefix_chars to
categorize arguments as optional/positional
chars = self.prefix_chars
if not args or len(args) == 1 and args[0][0] not in chars:
see also _get_optional_kwargs method.
class _ArgumentGroup(_ActionsContainer):
inherits from _ActionsContainer, and usually gets the prefix_chars from its
container (the parser)
update('prefix_chars', container.prefix_chars)
The parser is created with
class ArgumentParser(_AttributeHolder, _ActionsContainer):
and documents the use of prefix_chars.
In addition to passing prefix_chars to its Super, it uses
default_prefix = '-' if '-' in prefix_chars else prefix_chars[0]
to define the -h help argument.
Early in parsing, args strings are categorized as 'O' or 'A'. That is done in,
which uses:
def _parse_optional(self, arg_string):
# if it doesn't start with a prefix, it was meant to be positional
if not arg_string[0] in self.prefix_chars:
return None
def _get_option_tuples(self, option_string):
also uses the parser's own prefix_chars.
During parsing (several layers down)
def consume_optional(start_index):
# if the action is a single-dash option and takes no
# arguments, try to parse more single-dash options out
# of the tail of the option string
chars = self.prefix_chars
if arg_count == 0 and option_string[1] not in chars:
Here, the parser's own prefix_chars is used to handle the chained short-dash
options.
---
In sum, while Argument_Group can have its own prefix_chars, that is only used
for help formatting. It's the parser's prefix_chars that is used when parsing.
The group's chars is ignored.
The _ArgumentGroup__init__ suggests something more than simple inheritance may
have been intended for prefix_chars, but in practice all it affects is the
help.
I haven't seen this issue raised before, and since this group parameter is not
documented, I think it's safe to ignore it.
An alternative is to have add_argument_group (or _ArgumentGroup__init__)
explicitly reject the prefix_chars parameter.
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue45656>
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