[PyQt] PyQt4 and Python 3.0

[Phil Thompson]

On Fri, 03 Oct 2008 16:45:12 -0700, Glenn Linderman <glenn at nevcal.com>
wrote:
> On approximately 10/3/2008 4:25 PM, came the following characters from 
> the keyboard of Phil Thompson:
>> Personally I think "compatibility wrappers" are a waste of time and
>> effort.
>> There are times when you really should rewrite your application (and I
>> don't care how big it is). PyQt4 is a complete rewrite of PyQt3, SIP5
>> will
>> not share any code with SIP4.
>>   
> 
> Interesting philosophy.  Some truth there.  But then it is a big job to 
> do a rewrite, and someone else's release schedule isn't always the right 
> time.

You have a potential problem if one customer wants your app for Py2 and
another for Py3. In reality I don't see that as a major problem as paying
customers are going to be the most conservative. I think it will be a while
before Py3 becomes mainstream.

>> Major transitions (Qt3 => Qt4, Python2 => Python3) should be considered
>> as
>> opportunities for rewrites. They should not be treated as "how can I get
>> from one to the other with as few changes as possible".
>>   
> 
> If the application was old, I might agree.  But here I am, thinking 
> about, and starting to code, a brand new application.
> 
>> Therefore, to answer your specific question, if you need to deploy your
>> application within 6 months (as a minimum) then write for Python2. If
you
>> do then don't bother trying to write it with Python3 in mind. By the
time
>> you get to the point when you want a Python3 version you will have
>> realised
>> how badly you wrote it in the first place that you will want to rewrite
>> it
>> anyway.
>>   
> 
> So say I wish to deploy in 8 months (the reality is, it will be deployed 
> when it is ready, if not sooner, and that depends on how things go with 
> some other projects also)...  I'd like to avoid deploying it twice in 
> succession on different platforms within a couple months... and even if 
> it was deployed in 4 months, I'd hardly know what to rewrite by then.

Unless your have specific customer demands as I mentioned above, then its
up to you what you deploy.

>> On the other hand, if you did write it correctly in the first place
>> (something I've never managed) PyQt4 for Python2 will be maintained for
>> several years - certainly while new versions of Python2 are released.
>>   
> 
> So this implies, just build it for Python 2 and deploy it, and if it 
> works well enough, leave it there until I figure out what rewrites are 
> necessary.  Certainly possible, but I'm already tired of putting "u" in 
> front of my string constants

Which you don't need to do.

> and of converting from QString back to 
> unicode...

...and avoiding that will be a benefit of moving to PyQt for Py3. It's up
to you.

Obviously you can take sensible steps when designing your app to minimise
the changes - keep your GUI code separate from your models and business
logic, add some "compatibility wrapper" stuff that makes sense in the
context of your own app.

What I will try and do - probably via the wiki - is to document what the
incompatibilities will be (though it will be a moving target) so that
people can try and write for both Py2 and Py3 if that's appropriate for
their app.

Phil