argparse.ArgumentParser("blah")

[Peter Otten]

Roy Smith wrote:

> As I read the docs (http://tinyurl.com/3ww9scr), the following two calls
> should result in the same object:
> 
> parser = argparse.ArgumentParser(description="blah")
> parser = argparse.ArgumentParser("blah")
> 
> In the first case, I'm explicitly setting description to "blah", in the
> second case, I'm passing "blah" as a positional parameter so it should
> be taken as first parameter to the function, which happens to be
> description.  Either way should end up the same.
> 
> I don't, however, get the same behavior when run with "-h".  The first
> gives what I would expect:
> 
> ------------------------------------------------
> usage: arg.py [-h]
> 
> blah
> 
> optional arguments:
>   -h, --help  show this help message and exit
> ------------------------------------------------
> 
> and the second gives:
> 
> ------------------------------------------------
> usage: blah [-h]
> 
> optional arguments:
>   -h, --help  show this help message and exit
> ------------------------------------------------
> 
> Is this a bug, or am I just not reading the docs right?

A quick look into the source code reveals the the documentation is not 
consistent with the actual implementation:

http://hg.python.org/cpython/file/eef1027ab2f0/Lib/argparse.py#l1581

"""
class ArgumentParser(_AttributeHolder, _ActionsContainer):
[...]
    def __init__(self,
                 prog=None,
                 usage=None,
                 description=None,
                 epilog=None,
                 version=None,
                 parents=[],
                 formatter_class=HelpFormatter,
                 prefix_chars='-',
                 fromfile_prefix_chars=None,
                 argument_default=None,
                 conflict_handler='error',
                 add_help=True):
"""

I suggest that you file a bug report.

PS: My guess is that you are supposed to use keyword parameters only, but 
that the implementation doesn't enforce that (yet?).