Inconsistent hash output for _Comment and _Element

[Cindy]

__hash__ output is inconsistent causing my dictionary using the _Comment as the key to be unusable. The same thing was happening with the _Element __hash__ but I am unable to reproduce it at the moment.

test.xml:
<Test>
    <!--
        A comment.
    -->
</Test>

OS: Windows 7, IDLE - Python 2.7.12 Shell output:
>>> from lxml import etree
>>> parser = etree.XMLParser(strip_cdata=False, recover=True, encoding='UTF-8')
>>> new_xml = etree.parse('test.xml', parser)
>>> c = new_xml.getroot()
>>> lxml.etree._Comment.__hash__(c[0])
-2144458933
>>> lxml.etree._Comment.__hash__(c[0])
3024733
>>> lxml.etree._Comment.__hash__(c[0])
3024738
>>> c[0]
<!--\n A comment.\n -->

[scoder (scoder)]

This works as (currently) designed. Elements (and Comments) don't implement their own hash function, which means that they hash by their object ID. These objects get created on the fly, which shows in your example. You are simply hashing three different objects.

I would consider a pull request, though, that implements a hash function based on the underlying libxml2 node pointer (i.e. the "_c_node" attribute).