On 1/6/2015 7:39 AM, Victor Stinner wrote:

More context:

2014-12-19 12:43 GMT+01:00 anatoly techtonik :

...

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 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

I thought of this exact comment when I read the "bug fix considered a regression." On Tue, Jan 6, 2015 at 2:41 PM, Guido van Rossum wrote:

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

On Tue, Jan 6, 2015 at 12:25 PM, Terry Reedy wrote:

...

On 1/6/2015 7:39 AM, Victor Stinner wrote:

...

More context:

2014-12-19 12:43 GMT+01:00 anatoly techtonik :

...

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 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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