[Python-Dev] python 2.7.9 regression in argparse?

Victor Stinner victor.stinner at gmail.com
Tue Jan 6 13:39:13 CET 2015

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
#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,
+        # 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.


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