[Python-Dev] Python 2.7b1 and argparse's version action (original) (raw)

Tobias Herp Tobias.Herp at gmx.de
Sun Apr 18 12:31:02 CEST 2010

Hi, all,

(I don't know whether the first attempt to post this went through; I could'nt find it, so I retry. My apologies for any inconvenience...)

I noticed that Python 2.7 beta 1 now contains the argparse module, which might be a good thing. The code has been cleaned up, too, compared to the current version 1.1.

But there is still one issue with argparse; to tell the story from the beginning:

The ArgumentParser class uses uses '-v' as a default short option for the 'tell me the program version' facility. Since this is commonly used for verbosity, and the vast majority of *X commandline tools use '-V' instead (if they bother to accompany '--version' with a short option at all). Therefore I submitted an issue report at

<http://code.google.com/p/argparse/issues/detail?id=43>.

To put it short: Argparse should simply do this like optparse does already. I.e., use '--version', '--help' and '-h' by default, but not '-v'.

Subsequently I spent a hard time arguing. (Perhaps it was somewhat distracting that I proposed a way of postponing the creation of the help and version options and to provide them with the short options which are left unused e.g. for hosts (database clients), human readability (ls, du, etc.) or verbosity; Steven had stated it might break backward compatibility if the '-v' option string for version output would be dropped which might be relied on by other programs which parse the output. IMO, however, anyone should be beaten who relies on '-v' giving the version while '--version' has been present all the time. The Zen of Python, 2nd aphorism: "Explicit is better than implicit")

What happened was the following: Completely unnecessarily, the 'version' constructor argument is now deprecated. This fact doesn't solve any problem I can think of; the only effect is to make programming more cumbersome, and it is /one more/ difference to optparse.

The 'version' argument is a perfectly reasonable way to provide a script with a simple version information feature. Of course, it should only define the '--version' argument; it must not define '-v' for this purpose, since this is commonly used for verbosity, and '-V' is widely used to accompany '--version'. I have lots of scripts which use optparse, and every single one uses the version argument. I consider this a matter of good style.

The deprecation of the 'version' argument press-gangs people to replace it by parser.add_argument('--version', action='version', version='', # the only common part help="show program's version number and exit") in every single script (which violates the DRY principle, by the way).

Of course, if a more fancy version information is needed, e.g. reporting the versions of all imported modules, it is perfectly possible to just omit the version argument during creation and build a special 'version' action. No deprecation warnings are needed for this.

Before Python 2.7 reaches productivity stage, IMNSHO the following changes should be applied to argparse.py:

This is a very simple thing to do; I'd happily provide a patch. (The only complicated task might be to make the unit tests reflect the change; but for a start, 7 lines of the test_main function could be dropped.)

Just for the records, this is what optparse does:

What do you think?

--

Cheers, Tobias

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