[Cython] CmdLine.py refactoring

[Stefan Behnel]

Dag Sverre Seljebotn, 09.08.2011 08:51:
> On 08/09/2011 08:33 AM, Stefan Behnel wrote:
>> Stefano, 08.08.2011 22:36:
>>> As a proof of its quality, Fedora, Ubuntu and SuSe all ship a
>>> python-argparse
>>> package for older versions of python (<2.7). Given that the module is
>>> self-
>>> contained and as small as 80KB, wouldn't be feasible to add it as a build
>>> dependency?
>>
>> Note that that's huge compared to the current command line parser. The
>> current implementation doesn't even use 8K, and it's perfectly
>> self-contained as well.
>
> I'd prefer if optparse was sufficient. The main advantage of argparse to me
> seems to be in parsing command structures, such as "hg add ...", "hg init
> ...". Since we don't do that in Cython I'd think optparse would be
> sufficient, and that we should not ship argparse.

Agreed. I never understood why the CPython devs decided to deprecate 
optparse in 2.7.


>> Could you try to explain what the advantages of your new implementation
>> are?
>
> Assuming one switches to optparse, I find this line of reasoning highly
> dubious... and think the burden should be the other way: Please argue why
> custom, specific, low-level code is necesarry in Cython's command line parser.

Since Stefano has decided to write the code, I think the "it's there and it 
works" argument is basically dead already. And I do see the advantage of 
using the "standard" tool for the job.

However, I also see the problem that optparse is deprecated and may get 
removed in a future 3.x version. So, switching to optparse now means that 
we may have to switch to something else later, whereas that's not the case 
with the current code, however clumsy and low-level it may be.

 From a look at Stefano's code, it seems that it's not all that hard to 
support both argparse and optparse. If we can keep that up, that would 
solve the future upgrade problem.

I actually think that the new implementation looks much clearer than what 
we currently have:

https://github.com/satufk/cython/blob/13309377dd3fd90761e97718fc3297efe1e962dc/Cython/Compiler/CmdLine.py


> Using optparse/argparse have the obvious benefits that they are higher
> level and so more stuff can be automated. In particular, better
> automatically up-to-date command line help tracking changes elsewhere in
> the codebase (such as directives that can be passed to -X).

Yes, the list of "-X" options in the cmd line help text should be 
automatically generated from the Options. And, yes, the current status of 
the help text suggests that it does represent a notable maintenance 
overhead to keep it up to date with the implementation.

Stefan