replace getiterator function for Python 3.6

[brandonchinn178]

Fixes #499

The getiterator function doesn't accept arguments in Python 3.6 (raises a TypeError), so this manually filters elements based on the tag name

[waylan]

Thanks for doing the work on this. I don't doubt your right, but did you find any comments about this change in Python's documentation/release notes/commit logs? I'm curious about the reasoning behind that change.

[brandonchinn178]

There are no explicit changes in the changelog, so I suspect there must've been some change in the way Python 3.6 interfaces with the underlying C library?

[mitya57]

The documentation for 3.6 still mentions tag as a valid argument.

According to the stacktraces this looks like a bug in Python 3.6 to me:

>>> from xml.etree.ElementTree import Element
>>> el = Element('foo')
>>> el.getiterator('bar')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: ../Python/getargs.c:1508: bad argument to internal function
>>> el.getiterator(tag='bar')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: iter() takes at most 1 argument (140172072006928 given)

Please report it to Python issue tracker (or I can do it for you, if you prefer).

[brandonchinn178]

Wait so .iter('div') works... since getiterator is being deprecated anyway, I think this is a worthwhile change. It seems like maybe there's a bug in getiterator when it passes the call to iter?

[waylan]

Ah, getiterator has been deprecated since Python 2.7, and iter was added in 2.7. As 2.7 is the lowest supported version, we should be using iter.

[mitya57]

Getting rid of deprecated calls is indeed the good thing.
But I filed http://bugs.python.org/issue28314 for the regression anyway.