In file included from src/lxml/lxml.etree.c:239:0:

/tmp/pip_build_root/lxml/src/lxml/includes/etree_defs.h:14:31: fatal error: libxml/xmlversion.h: No such file or directory

compilation terminated.

error: command 'gcc' failed with exit status 1

----------------------------------------
Rolling back uninstall of lxml

sudo apt-get install libxml2-dev libxslt-dev python-dev