[New-bugs-announce] [issue16308] Undocumented (?) behaviour change in argparse from 3.2.3 to 3.3.0

[telmich]

New submission from telmich:

Using argparse with subparsers, the default behaviour if no subparser was selected, was to print help:

cdist% git describe 
2.0.14-59-g5315c41
cdist% ./bin/cdist 
usage: cdist [-h] [-d] [-v] [-V] {banner,config} ...
cdist: error: too few arguments
cdist% python3 -V 
Python 3.2.3

With python 3.3.0, this changed and thus the so far uncalled code block is executed:

cdist% ./bin/cdist  
Traceback (most recent call last):
  File "./bin/cdist", line 237, in <module>
    commandline()
  File "./bin/cdist", line 104, in commandline
    args.func(args)
AttributeError: 'Namespace' object has no attribute 'func'
cdist% git describe 
2.0.14-59-g5315c41
cdist% python3 -V
Python 3.3.0


Question:

What is the correct way now to abort, if no subparser or
no option was given (i.e. restore the previous behaviour)?

I tried to fix this problem by using

parser['main'].set_defaults(func=commandline_main)

to setup a default handler for main, but this overwrites the func= parameter for all subparsers as well and thus renders this possibility useless (commits b7a8a84 and 840dbc5 in cdist).

The source code for cdist using the subparsers is available at http://git.schottelius.org/?p=cdist

----------
components: Library (Lib)
messages: 173659
nosy: telmich
priority: normal
severity: normal
status: open
title: Undocumented (?) behaviour change in argparse from 3.2.3 to 3.3.0
versions: Python 3.3

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16308>
_______________________________________