[Python-Dev] [Python-checkins] cpython (merge 3.2 -> default): - Issue #15906: Fix a regression in argparse caused by the preceding change,

[Chris Jerdonek]

On Tue, Sep 11, 2012 at 9:13 PM, barry.warsaw
<python-checkins at python.org> wrote:
> http://hg.python.org/cpython/rev/25e41fdc4e60
> changeset:   79001:25e41fdc4e60
> parent:      78998:6fea947edead
> parent:      79000:bc342cd7ed96
> user:        Barry Warsaw <barry at python.org>
> date:        Wed Sep 12 00:12:29 2012 -0400
> summary:
>   - Issue #15906: Fix a regression in argparse caused by the preceding change,
>   when action='append', type='str' and default=[].

I didn't have time to respond Barry's e-mail from four hours ago
before this was committed.  I think this change may be problematic.
At the least, I think people should have an opportunity to air their
specific concerns and talk through the implications.

Also, from the discussion it seemed like the sentiment was leaning
towards a different approach for the fix.

I made a comment on the issue with some more extended remarks:

http://bugs.python.org/msg170351

--Chris


>
> files:
>   Lib/argparse.py           |   1 +
>   Lib/test/test_argparse.py |  10 ++++++++++
>   Misc/NEWS                 |   3 +++
>   3 files changed, 14 insertions(+), 0 deletions(-)
>
>
> diff --git a/Lib/argparse.py b/Lib/argparse.py
> --- a/Lib/argparse.py
> +++ b/Lib/argparse.py
> @@ -1961,6 +1961,7 @@
>                      # twice (which may fail) if the argument was given, but
>                      # only if it was defined already in the namespace
>                      if (action.default is not None and
> +                        isinstance(action, _StoreAction) and
>                          hasattr(namespace, action.dest) and
>                          action.default is getattr(namespace, action.dest)):
>                          setattr(namespace, action.dest,
> diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
> --- a/Lib/test/test_argparse.py
> +++ b/Lib/test/test_argparse.py
> @@ -4607,6 +4607,16 @@
>          args = parser.parse_args([])
>          self.assertEqual(NS(foo='foo_converted'), args)
>
> +    def test_issue_15906(self):
> +        # Issue #15906: When action='append', type=str, default=[] are
> +        # providing, the dest value was the string representation "[]" when it
> +        # should have been an empty list.
> +        parser = argparse.ArgumentParser()
> +        parser.add_argument('--test', dest='test', type=str,
> +                            default=[], action='append')
> +        args = parser.parse_args([])
> +        self.assertEqual(args.test, [])
> +
>  # ======================
>  # parse_known_args tests
>  # ======================
> diff --git a/Misc/NEWS b/Misc/NEWS
> --- a/Misc/NEWS
> +++ b/Misc/NEWS
> @@ -56,6 +56,9 @@
>    especially problematic for the FileType type, as a default file would always
>    be opened, even if a file argument was specified on the command line.
>
> +- Issue #15906: Fix a regression in argparse caused by the preceding change,
> +  when action='append', type='str' and default=[].
> +
>  Extension Modules
>  -----------------
>
>
> --
> Repository URL: http://hg.python.org/cpython
>
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