Support Python 3, drop support for Python < 2.6

[Barry Warsaw]

This needs to be ported to Python 3 as a dependency for LP: #1096512

[Barry Warsaw (barry)]

On Jan 06, 2013, at 04:10 AM, William Grant wrote:

>If we're dropping <2.6 support we could switch it to use class
>decorators instead.

We'll have to anyway for zope.interface implements() calls, since Python 3
only supports @implementor class decorators.

[Barry Warsaw (barry)]

Well, hmm... this seems to be a big problem:

File "/home/barry/projects/lazr/lp1096513/src/lazr/delegates/README.rst", line 63, in README.rst
Failed example:
    class SomeClass(object):
        delegates(IFoo)
        def __init__(self, context):
            self.context = context
Exception raised:
    Traceback (most recent call last):
      File "/usr/lib/python3.3/doctest.py", line 1287, in __run
        compileflags, 1), test.globs)
      File "<doctest README.rst[6]>", line 1, in <module>
        class SomeClass(object):
      File "<doctest README.rst[6]>", line 2, in SomeClass
        delegates(IFoo)
      File "/home/barry/projects/lazr/lp1096513/src/lazr/delegates/_delegates.py", line 91, in delegates
        addClassAdvisor(_delegates_advice, depth=2)
      File "/home/barry/projects/lazr/lp1096513/zope.interface-4.0.3-py3.3-linux-x86_64.egg/zope/interface/advice.py", line 100, in addClassAdvisor
        raise TypeError('Class advice impossible in Python3')
    TypeError: Class advice impossible in Python3

[William Grant (wgrant)]

If we're dropping <2.6 support we could switch it to use class decorators instead.

[Barry Warsaw (barry)]

So here's what I came up with.

@delegate_to(IFoo)
class Whatever:

@delegate_to(IFoo, context='myfoo')

@delegate_to(IFoo0, IFoo1, IFoo2, context='myfoo')

I like the API, but I suppose you could quibble over `delegate_to`. It has to be different from `delegates` for backward compatibility (which still works, but of course only in Python 2), and I tried `delegation`, `delegater`, and `delegates_to`, and this one reads the best to me.

FWIW, the class decorator works in Python 2.6, 2.7, 3.2, and 3.3. I completely rewrote the usage.rst file to only describe the class decorator, but I moved all the old api tests to unittest files. 100% coverage on all Pythons.

I made many of the same other changes (getting rid of buildout, switching to nosetests, etc.) that I made to lazr.smtptest.

[Barry Warsaw (barry)]

On Jan 07, 2013, at 12:08 AM, Barry Warsaw wrote:

>I like the API, but I suppose you could quibble over `delegate_to`. It
>has to be different from `delegates` for backward compatibility (which
>still works, but of course only in Python 2), and I tried `delegation`,
>`delegater`, and `delegates_to`, and this one reads the best to me.

@delegating(IFoo) ... ?