[Python-Dev] Python 2.7b1 and argparse's version action

[Tobias Herp]

Steven Bethard schrieb:
> On Sun, Apr 18, 2010 at 3:31 AM, Tobias Herp <Tobias.Herp at gmx.de> wrote:
>> 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'.
> [snip]
>> What happened was the following:
>> Completely unnecessarily, the 'version' constructor argument is now
>> deprecated.
> [snip]
>> The deprecation of the 'version' argument press-gangs people to replace
>> it by
>>  parser.add_argument('--version', action='version',
>>                      version='<the version>',    # the only common part
>>                      help="show program's version number and exit")
> 
> What Tobias has conveniently omitted is that there was not much
> agreement on what the default behavior of the version flag should be.

Well, the mail was quite long already, and the issue-tracker issue was
linked.

> Things that were proposed:
> 
> * Use both -v and --version

This is very unusual. I don't know of a single example other than
existing argparse.  Incompatible to existing optparse usage.

> * Use both -V and --version

A very common combination; many programs which support --version
accompany it with -V.
However, if we'd add '-V' to the default option strings, we would likely
break existing programs which worked around the so-far default.

> * Use just --version

IMO the only way, and the way optparse does it.

> * Print out just the version string
> * Print out program name with the version string

If this is an issue:  With optparse, the version argument value is
printed, which is often something like '%prog '+VERSION
(for argparse, '%(prog)s '+VERSION or '%%(prog)s %s' % VERSION).
This way, the decision is left to the programmer.
Completely agreeable, as far as I'm concerned.

> I put up a poll [...]
> 
> Given the lack of consensus, the many
> different options people thought were the "right" way to do things,
> and the fact that the action='version' approach allows people to
> customize the flags to whatever they want, I stick by my decision to
> deprecate the constructor argument ...

A. Very. Bad. Idea.

> ... and redirect people to the more flexible add_argument approach.

It is ok to /allow/ people to customize the flags to whatever they want.
It is /not/ ok to /force/ them to do so, if there is a perfectly
reasonable solution which allows them to stick with their habits.
And there is one: drop the '-v' default.  The only way (see above).

> In the face of ambiguity, refuse the temptation to guess.

No guessing is needed (and the ZoP aphorism is not applicable here: this
is not about guessing what the user might have meant.  Besides, if the
user specifies '--version', [s]he /very/ likely wants some info about
the program version; giving '-v' can have been done looking forward to
--verbose output (ok, nothing bad will happen, but it mismatches user
expectations).

> In general, I should say that I'm not opposed to changing the behavior
> in Python trunk, even if it causes a bit of backwards incompatibility.

A /very little/ bit.
When fetching stdout to get the program version, it is much more
reasonable to rely on '--version' than on '-v'.  This is /the/ option
string which is best supported by far.

> But I'd really like a consensus about the correct behavior, and so far
> I have not seen that.

We'll have one ;-)

-- 
Tobias