bpo-39546: argparse: Honor allow_abbrev=False for specified prefix_chars (GH-18337)
When `allow_abbrev` was first added, disabling the abbreviation of
long options broke the grouping of short flags ([bpo-26967](https://bugs.python.org/issue26967)). As a fix,
b1e4d1b603 (contained in v3.8) ignores `allow_abbrev=False` for a
given argument string if the string does _not_ start with "--"
(i.e. it doesn't look like a long option).
This fix, however, doesn't take into account that long options can
start with alternative characters specified via `prefix_chars`,
introducing a regression: `allow_abbrev=False` has no effect on long
options that start with an alternative prefix character.
The most minimal fix would be to replace the "starts with --" check
with a "starts with two prefix_chars characters". But
`_get_option_tuples` already distinguishes between long and short
options, so let's instead piggyback off of that check by moving the
`allow_abbrev` condition into `_get_option_tuples`.
https://bugs.python.org/issue39546
diff --git a/Lib/argparse.py b/Lib/argparse.py
index 5d3ce2a..9c710ce 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -2199,24 +2199,23 @@
action = self._option_string_actions[option_string]
return action, option_string, explicit_arg
- if self.allow_abbrev or not arg_string.startswith('--'):
- # search through all possible prefixes of the option string
- # and all actions in the parser for possible interpretations
- option_tuples = self._get_option_tuples(arg_string)
+ # search through all possible prefixes of the option string
+ # and all actions in the parser for possible interpretations
+ option_tuples = self._get_option_tuples(arg_string)
- # if multiple actions match, the option string was ambiguous
- if len(option_tuples) > 1:
- options = ', '.join([option_string
- for action, option_string, explicit_arg in option_tuples])
- args = {'option': arg_string, 'matches': options}
- msg = _('ambiguous option: %(option)s could match %(matches)s')
- self.error(msg % args)
+ # if multiple actions match, the option string was ambiguous
+ if len(option_tuples) > 1:
+ options = ', '.join([option_string
+ for action, option_string, explicit_arg in option_tuples])
+ args = {'option': arg_string, 'matches': options}
+ msg = _('ambiguous option: %(option)s could match %(matches)s')
+ self.error(msg % args)
- # if exactly one action matched, this segmentation is good,
- # so return the parsed action
- elif len(option_tuples) == 1:
- option_tuple, = option_tuples
- return option_tuple
+ # if exactly one action matched, this segmentation is good,
+ # so return the parsed action
+ elif len(option_tuples) == 1:
+ option_tuple, = option_tuples
+ return option_tuple
# if it was not found as an option, but it looks like a negative
# number, it was meant to be positional
@@ -2240,16 +2239,17 @@
# split at the '='
chars = self.prefix_chars
if option_string[0] in chars and option_string[1] in chars:
- if '=' in option_string:
- option_prefix, explicit_arg = option_string.split('=', 1)
- else:
- option_prefix = option_string
- explicit_arg = None
- for option_string in self._option_string_actions:
- if option_string.startswith(option_prefix):
- action = self._option_string_actions[option_string]
- tup = action, option_string, explicit_arg
- result.append(tup)
+ if self.allow_abbrev:
+ if '=' in option_string:
+ option_prefix, explicit_arg = option_string.split('=', 1)
+ else:
+ option_prefix = option_string
+ explicit_arg = None
+ for option_string in self._option_string_actions:
+ if option_string.startswith(option_prefix):
+ action = self._option_string_actions[option_string]
+ tup = action, option_string, explicit_arg
+ result.append(tup)
# single character options can be concatenated with their arguments
# but multiple character options always have to have their argument