[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[Rémi Lapeyre]

Change by Rémi Lapeyre :


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versions: +Python 3.10, Python 3.9 -Python 2.7

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[hai shi]

hai shi  added the comment:

oh, sorry, pls ignore it. I misunderstand your opinion.

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type: crash -> behavior

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[hai shi]

Change by hai shi :


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pull_requests: +15323
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/15656

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Why did you switch back to "crash"?

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[hai shi]

hai shi  added the comment:

Thanks, Raymond. This patch not a formal patch, just show what i want to do. if 
everything agree this behavior, I would add a normal PR.

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type: behavior -> crash

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[Raymond Hettinger]

Raymond Hettinger  added the comment:

FWIW, raising an uncaught exception isn't what we normally consider a "crash".  
We typically save that designation for segfaults.

Ideally, a good patch/pr will also have tests.

Also, given the rarity of the exception, I would be reserved about backporting, 
keeping it to 3.8 and 3.9.

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nosy: +rhettinger
type: crash -> behavior

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[hai shi]

hai shi  added the comment:

Adding a judgment of explicit_args in judgment statement in the patch.

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keywords: +patch
Added file: https://bugs.python.org/file48582/parse_v1.patch

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[hai shi]

hai shi  added the comment:

I do something such as:
p = argparse.ArgumentParser()
p.add_argument('-a', action='store_true')
p.add_argument('-b', action='store_true')
p.parse_args('-ab='.split())

thos code code jump in 1903, and the explicit_arg's value is: 'b='

1901   action_tuples.append((action, [], option_string))
1902   char = option_string[0]
1903   option_string = char + explicit_arg[0]

IMHO, we should judge this explicit_arg's value before jump this judgment 
statement.

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nosy: +shihai1991

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +xtreak
versions: +Python 2.7, Python 3.7, Python 3.8

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[issue36267] User input to argparse raises Index_Error: "-a=" on a 'store_true' action

[paul j3]

New submission from paul j3 :

Test case:

parser = argparse.ArgumentParser()
parser.add_argument("-a", action="store_true")
args = parser.parse_args("-a=".split())

raises an Index_Error, which is not caught by the argparse error mechanism.

This is an unusual case, the coincidence of several user errors - 'store_true' 
which shouldn't take an argument and a short optional with a bare =.  So it's 
unlikely to occur.  Still, argparse shouldn't ever respond to a command line 
value with an uncaught error.

The traceback shows that it occurs during the handling of the explicit_arg in 
consume_optional.

Traceback (most recent call last):
  File "argparseRaiseIndexError.py", line 5, in 
args = parser.parse_args("-a=".split())
  File "/usr/lib/python3.6/argparse.py", line 1743, in parse_args
args, argv = self.parse_known_args(args, namespace)
  File "/usr/lib/python3.6/argparse.py", line 1775, in parse_known_args
namespace, args = self._parse_known_args(args, namespace)
  File "/usr/lib/python3.6/argparse.py", line 1981, in _parse_known_args
start_index = consume_optional(start_index)
  File "/usr/lib/python3.6/argparse.py", line 1881, in consume_optional
option_string = char + explicit_arg[0]
IndexError: string index out of range

The issue was raised in a Stackoverflow question, where I and the poster 
explore why it occurs, and possible fixes.

https://stackoverflow.com/questions/54662609/python-argparse-indexerror-for-passing-a

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components: Library (Lib)
messages: 337709
nosy: paul.j3
priority: normal
severity: normal
stage: needs patch
status: open
title: User input to argparse raises Index_Error:  "-a=" on a 'store_true' 
action
type: crash

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