[Python-Dev] python 2.7.9 regression in argparse?

[Guido van Rossum]

There's an obligatory XKCD reference for this: http://xkcd.com/1172/

On Tue, Jan 6, 2015 at 12:25 PM, Terry Reedy <tjreedy at udel.edu> wrote:

> On 1/6/2015 7:39 AM, Victor Stinner wrote:
>
>> More context:
>>
>> 2014-12-19 12:43 GMT+01:00 anatoly techtonik <techtonik at gmail.com>:
>>
>>> https://github.com/nickstenning/honcho/pull/121
>>>
>>
>> The link mentions the following changeset:
>> ---
>> changeset:   93122:1a3143752db2
>> branch:      2.7
>> parent:      93112:927cca0b9337
>> user:        R David Murray <rdmurray at bitdance.com>
>> date:        Fri Oct 17 20:07:08 2014 -0400
>> files:       Lib/argparse.py Lib/test/test_argparse.py Misc/NEWS
>> description:
>> #9351: set_defaults on subparser is no longer ignored if set on parent.
>>
>> Before, if a default was set on the parent parser, any default for that
>> variable set via set_defaults on a subparser would be ignored.  Now
>> the subparser set_defaults is honored.
>>
>> Patch by Jyrki Pullianinen.
>>
>>
>> diff -r 927cca0b9337 -r 1a3143752db2 Lib/argparse.py
>> --- a/Lib/argparse.py   Fri Oct 17 16:20:15 2014 -0500
>> +++ b/Lib/argparse.py   Fri Oct 17 20:07:08 2014 -0400
>> @@ -1089,7 +1089,14 @@ class _SubParsersAction(Action):
>>           # parse all the remaining options into the namespace
>>           # store any unrecognized options on the object, so that the top
>>           # level parser can decide what to do with them
>> -        namespace, arg_strings = parser.parse_known_args(arg_strings,
>> namespace)
>> +
>> +        # In case this subparser defines new defaults, we parse them
>> +        # in a new namespace object and then update the original
>> +        # namespace for the relevant parts.
>> +        subnamespace, arg_strings = parser.parse_known_args(arg_strings,
>> None)
>> +        for key, value in vars(subnamespace).items():
>> +            setattr(namespace, key, value)
>> +
>>           if arg_strings:
>>               vars(namespace).setdefault(_UNRECOGNIZED_ARGS_ATTR, [])
>>               getattr(namespace, _UNRECOGNIZED_ARGS_ATTR).
>> extend(arg_strings)
>> ---
>>
>> Which is related to http://bugs.python.org/issue9351
>>
>> Maybe argparse just became more strict? I don't understand the issue.
>>
>
> Steven Bethard, the argparse maintainer, defined the old behavior of
> ignoring subparser defaults (where there are also top level defaults) as a
> bug "counter to what people probably expect".  If the old behavior had been
> documented, changing it in a bug-fix release would have been a mistake.
> But looking at the patch, the doc seems to have been silent on the issue.
>
> This is not the first time someone considered a 'bug fix' to be a
> 'regression', which it might be from their viewpoint.  The last comment on
> the github thread suggests that an easy fix was found.
>
> --
> Terry Jan Reedy
>
>
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-- 
--Guido van Rossum (python.org/~guido)
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