[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[paul j3]

Change by paul j3 :


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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[paul j3]

paul j3  added the comment:

>From the documentation, 16.4.4.1. Option value syntax

> For short options (options only one character long), the option and its value 
> can be concatenated:

> Several short options can be joined together, using only a single - prefix, 
> as long as only the last option (or none of them) requires a value:

It does not promise that an short option and an unrelated (not-required) value 
will work.  The only value that works in such a construct is one required by 
the last short option.

I think this should be closed, unless you can support your expectations from 
documentation, or examples from other parsers.

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[Yauhen]

Yauhen  added the comment:

I am adding one more testcase in order to clarify more the problem:



import argparse
import sys

parser = argparse.ArgumentParser(prog=sys.argv[0], add_help=False)
parser.add_argument('-a', action='store_true')
parser.add_argument('-b', action='store_true')
parser.add_argument('-c', action='store_true')
parsed_args, unknown_args = parser.parse_known_args(sys.argv[1:])
print(parsed_args)
print(unknown_args)



$ python argparse_test.py -ab
Namespace(a=True, b=True, c=False)
[]


Expected result:
$ python argparse_test.py -ab -cd
Namespace(a=True, b=True, c=True)
['-d']

Actual result:
$ python argparse_test.py -ab -cd
usage: argparse_test.py [-a] [-b] [-c]
argparse_test.py: error: argument -c: ignored explicit argument 'd'

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[paul j3]

paul j3  added the comment:

Try adding a simple positional argument.  '-ab' would still produce this error.

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[paul j3]

paul j3  added the comment:

This error message is intentional.

In def consume_optional(start_index):

# identify additional optionals in the same arg string
# (e.g. -xyz is the same as -x -y -z if no args are required)

# 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:
action_tuples.append((action, [], option_string))
char = option_string[0]
option_string = char + explicit_arg[0]
new_explicit_arg = explicit_arg[1:] or None
optionals_map = self._option_string_actions
if option_string in optionals_map:
action = optionals_map[option_string]
explicit_arg = new_explicit_arg
else:
msg = _('ignored explicit argument %r')
raise ArgumentError(action, msg % explicit_arg)

In other words, it doesn't just split off that extra character and add it to 
'argument_strings' for further handling.

Either 'b' is an argument for the '-a' flag or it is a '-b' flag itself.  It 
can't be a positional or extra.

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[paul j3]

Change by paul j3 :


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nosy: +paul.j3

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[Terry J. Reedy]

Change by Terry J. Reedy :


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nosy: +bethard

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[Yauhen]

Yauhen  added the comment:

It was a mistake in expected result, should be:

$ python arparse_test.py -ab -c
Namespace(a=True)
['-b', '-c']

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[issue32756] argparse: parse_known_args: raising exception on unknown arg following known one

[Yauhen]

New submission from Yauhen :

steps to reproduce:

import argparse
import sys

parser = argparse.ArgumentParser(prog=sys.argv[0], add_help=False)
parser.add_argument('-a', action='store_true')
parsed_args, unknown_args = parser.parse_known_args(sys.argv[1:])
print(parsed_args)
print(unknown_args)


Expected result:

$ python arparse_test.py -ab
Namespace(a=True)
['b']


Actual result:

$ python arparse_test.py -ab
usage: arparse_test.py [-a]
arparse_test.py: error: argument -a: ignored explicit argument 'b'

--
components: Library (Lib)
messages: 311546
nosy: actionless
priority: normal
pull_requests: 5345
severity: normal
status: open
title: argparse: parse_known_args: raising exception on unknown arg following 
known one
versions: Python 3.6

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