Add support to parsing large xml inputs (https://github.com/RDFLib/rdflib/issues/749)

[artreven]

No description provided.

[gromgull]

This fails with huge_tree is not a valid keyword argument on all python versions.

We are quite lax with where we get elementtree from: https://github.com/RDFLib/rdflib/blob/master/rdflib/compat.py#L16-L36

I guess the default version doesn't support this?

[artreven]

I just checked what happens at my end: I use Python 3.5.2 and lxml 3.5.0. I get etree from lxml and the line etree.XMLParser(huge_tree=True) returns my the parser without any exceptions.
What could be the issue?

[niklasl]

As @gromgull says, the default etree from the standard library does not support this option:

import xml.etree.ElementTree as etree

etree.XMLParser(huge_tree=True)

On Python 3, this fails with:

Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
TypeError: 'huge_tree' is an invalid keyword argument for this function

Since lxml is an optional package for RDFLib, you cannot rely on it being available to support the non-standard keyword (huge_tree).

[coveralls]

Coverage increased (+1.2%) to 65.296% when pulling 85309a5 on artreven:master into ba4c542 on RDFLib:master.

[artreven]

Sorry, I did not get the original comment from @gromgull at first, I thought lxml is the default version. I have added an except clause to provide a fallback in case of default version.

[gromgull]

Thanks! (and sorry about the delay)