Apply 2to3 next fix.

[bfroehle]

Continuing on the Python 2/3 compatibility (which I'll refer to as '2and3') from #2095 and #2100, I propose to include the changes from running 2to3 -f next:

Converts the use of iterator’s next() methods to the next() function. It also renames next() methods to __next__().

One small issue is the behavior of next(x) on user defined classes:

Consider test_next.py

class X(object):
    def __init__(self, iterable):
        self.iterator = iter(iterable)
    def __iter__(self):
        return self
    def __next__(self):
        print("__next__ called")
        return next(self.iterator)
    def next(self):
        print("next called")
        return next(self.iterator)

x = X([1,2,3])
next(x)

And run it in Python 2.7 and 3.2:

$ python2.7 next_test.py
next called
$ python3.2 next_test.py
__next__ called

To work around this difference, I've just set next = __next__ manually after applying the 2to3 fix. This also maintains compatibility with any third party code which calls x.next().

[takluyver]

Test results for commit 360c5cd merged into master
Platform: linux2

• python2.7: OK (libraries not available: oct2py rpy2)
• python3.1: OK (libraries not available: cython matplotlib numpy oct2py pymongo qt rpy2 wx wx.aui zmq)
• python3.2: OK (libraries not available: cython oct2py pymongo rpy2 wx wx.aui)

Not available for testing: python2.6

[bfroehle]

Alternatively we could treat this as:

    def __next(self)__:
        # ...

    if not py3compat.PY3:
        next = __next__

This would make it more obvious what needs to be ripped out if Python 2 support was ever dropped...

[takluyver]

I think I'd side with doing that.

[bfroehle]

I agree. I've made the changes and pushed a new commit.

[takluyver]

Test results for commit 30e4a14 merged into master
Platform: linux2

• python2.7: OK (libraries not available: oct2py rpy2)
• python3.1: OK (libraries not available: cython matplotlib numpy oct2py pymongo qt rpy2 wx wx.aui zmq)
• python3.2: OK (libraries not available: cython oct2py pymongo rpy2 wx wx.aui)

Not available for testing: python2.6

[takluyver]

This looks OK to me. If no-one objects in about a day, we can merge it.

[minrk]

Is there a good reason that this method is defined in a conditional, and not just next = __next__? I know the method is not required in py3, but it seems cleaner to just define it.

[minrk]

Ah, now I just saw the conversation above. I don't really agree with the decision, but I don't feel strongly, so I'll go with you guys. Also, Python 2.6 testing is the most important here before merge.

[minrk]

Test results for commit 30e4a14 merged into master
Platform: darwin

• python2.6: OK (libraries not available: cython matplotlib oct2py pygments pymongo qt rpy2 tornado wx wx.aui)
• python2.7: OK (libraries not available: oct2py wx wx.aui)
• python3.2: OK (libraries not available: cython matplotlib oct2py pymongo qt rpy2 wx wx.aui)

Not available for testing: python3.1

[minrk]

2.6 is happy, +1 to merge.

[takluyver]

Merged - thanks.