[issue12353] argparse cannot handle empty arguments

[R. David Murray]

R. David Murray  added the comment:

Done.

--
resolution:  -> fixed
stage: test needed -> committed/rejected
status: open -> closed

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[issue12353] argparse cannot handle empty arguments

[Roundup Robot]

Roundup Robot  added the comment:

New changeset ac53876d1cc8 by R David Murray in branch '3.2':
#12353: argparse now correctly handles null argument values.
http://hg.python.org/cpython/rev/ac53876d1cc8

New changeset c4ad8a6eb0df by R David Murray in branch 'default':
Merge #12353: argparse now correctly handles null argument values.
http://hg.python.org/cpython/rev/c4ad8a6eb0df

New changeset c9806f0aaefb by R David Murray in branch '2.7':
#12353: argparse now correctly handles null argument values.
http://hg.python.org/cpython/rev/c9806f0aaefb

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nosy: +python-dev

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[issue12353] argparse cannot handle empty arguments

[Steven Bethard]

Steven Bethard  added the comment:

Yes, the original patch looks fine to me. I applied and tested it, and it works 
as expected.

Please go ahead and apply.

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[issue12353] argparse cannot handle empty arguments

[Zbyszek Szmek]

Changes by Zbyszek Szmek :


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nosy: +zbysz

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[issue12353] argparse cannot handle empty arguments

[Torsten Landschoff]

Torsten Landschoff  added the comment:

ping!?

I think this should be either applied or dropped. It does not make sense to 
have such a simple issue rot in the bug tracker...

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[issue12353] argparse cannot handle empty arguments

[R. David Murray]

R. David Murray  added the comment:

Actually, your original test might be fine.  Let me double check the test 
implementation.

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[issue12353] argparse cannot handle empty arguments

[R. David Murray]

R. David Murray  added the comment:

Ah, I see now.  I misread the original traceback.

Creating a new test case would be the appropriate way to go, given the 
structure of the argparse test suite.

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[issue12353] argparse cannot handle empty arguments

[Torsten Landschoff]

Torsten Landschoff  added the comment:

Here is another possible patch that will catch the problem.

But this enables the fromfile_prefix_chars option for all tests checking empty 
and space arguments. This way a problem that occurs only without that option 
might be hidden.

We would need to run those tests with and without fromfile_prefix_chars.

--
Added file: http://bugs.python.org/file22433/modify_test_empty.diff

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[issue12353] argparse cannot handle empty arguments

[Torsten Landschoff]

Torsten Landschoff  added the comment:

> Your unit test isn't consistent with the other unit tests in that set, which 
> makes me suspicious that it isn't testing what we need to test. 

That is because I did not try to understand the machinery behind the argparse 
unit tests completely. I did not want to create an extra unit test class just 
for this one test.

> Also, there are unit tests for this case further up in the test file 
> (TestEmptyAndSpaceContainingArguments).  I haven't been able to reproduce the 
> bug.

Did you run the unit tests from my patch?

> Can you post a short program that reproduces the failure?

Here you go:

from argparse import ArgumentParser
parser = ArgumentParser(fromfile_prefix_chars="@")
parser.parse_args([""])

This gives me

Traceback (most recent call last):
  File "", line 1, in 
  File "/opt/python3/lib/python3.3/argparse.py", line 1726, in parse_args
args, argv = self.parse_known_args(args, namespace)
  File "/opt/python3/lib/python3.3/argparse.py", line 1758, in parse_known_args
namespace, args = self._parse_known_args(args, namespace)
  File "/opt/python3/lib/python3.3/argparse.py", line 1770, in _parse_known_args
arg_strings = self._read_args_from_files(arg_strings)
  File "/opt/python3/lib/python3.3/argparse.py", line 2003, in 
_read_args_from_files
if arg_string[0] not in self.fromfile_prefix_chars:
IndexError: string index out of range

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[issue12353] argparse cannot handle empty arguments

[R. David Murray]

R. David Murray  added the comment:

Your unit test isn't consistent with the other unit tests in that set, which 
makes me suspicious that it isn't testing what we need to test.  Also, there 
are unit tests for this case further up in the test file 
(TestEmptyAndSpaceContainingArguments).  I haven't been able to reproduce the 
bug.

Can you post a short program that reproduces the failure?

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[issue12353] argparse cannot handle empty arguments

[Torsten Landschoff]

Torsten Landschoff  added the comment:

Here is an updated patch including unit test coverage.

--
keywords: +patch
nosy: +torsten
Added file: http://bugs.python.org/file22430/issue12353_test.diff

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[issue12353] argparse cannot handle empty arguments

[R. David Murray]

R. David Murray  added the comment:

Thanks for the report and patch.  I'm setting this to test needed since the 
final patch will need a unit test.

The idiomatic way to do this kind of check is 'if not argstring or 
arg_string[0] not in self.fromfile_prefix_chars):'

--
nosy: +bethard, r.david.murray
stage:  -> test needed
versions: +Python 3.2, Python 3.3

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[issue12353] argparse cannot handle empty arguments

[Bryan Jacobs]

New submission from Bryan Jacobs :

Parsing arguments with argparse fails with an IndexError when one of the 
arguments is the empty string (''). This is caused by an access to the zero'th 
element of the argument value, without a preceding length check.

Fixed by the below patch:

Index: Lib/argparse.py
===
--- Lib/argparse.py
+++ Lib/argparse.py
@@ -1967,7 +1967,7 @@ class ArgumentParser(_AttributeHolder, _
 for arg_string in arg_strings:
 
 # for regular arguments, just add them back into the list
-if arg_string[0] not in self.fromfile_prefix_chars:
+if len(arg_string) == 0 or arg_string[0] not in 
self.fromfile_prefix_chars:
 new_arg_strings.append(arg_string)
 
 # replace arguments referencing files with the file content

--
components: Library (Lib)
messages: 138515
nosy: bjacobs
priority: normal
severity: normal
status: open
title: argparse cannot handle empty arguments
type: behavior
versions: Python 2.7

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