Bug with LXML parser

[dmoklaf]

On some documents Trafilatura 0.6.0 fails with this error:

... File "/usr/local/Caskroom/miniconda/base/envs/myenv/lib/python3.7/site-packages/trafilatura/external.py", line 123, in sanitize_tree tree = prune_html(tree) File "/usr/local/Caskroom/miniconda/base/envs/myenv/lib/python3.7/site-packages/trafilatura/htmlprocessing.py", line 63, in prune_html element.drop_tree() AttributeError: 'lxml.etree._Element' object has no attribute 'drop_tree'

A git blame on this line reveals this is new code that has been made 21 days ago in this revision:
74444d2

Note: I am using the latest version of lxml (4.6.1)

[dmoklaf]

Further investigation reveals there might be 2 type of elements within the lxml library:
lxml.etree._Element (generated here by Trafilatura but that doesn't have the drop_tree method)
lxml.html.HtmlElement (that is not used here but has the drop_tree method called by Trafilatura)

[adbar]

Good catch, thank you!
As drop_tree results in a slight performance increase, I used a try-catch to make sure the error is taken into account: 7abe222