From --update on trytond_product

x86_64-linux-gnu-gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/tmp/pip_build_root/lxml/src/lxml/includes -I/usr/include/python2.7 -c src/lxml/lxml.etree.c -o build/temp.linux-x86_64-2.7/src/lxml/lxml.etree.o -w

src/lxml/lxml.etree.c:8:22: fatal error: pyconfig.h: No such file or directory

 #include "pyconfig.h"

                      ^

compilation terminated.

error: command 'x86_64-linux-gnu-gcc' failed with exit status 1

----------------------------------------
  Rolling back uninstall of lxml
Cleaning up...
Command /usr/bin/python -c "import setuptools, tokenize;__file__='/tmp/pip_build_root/lxml/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-iJ3Lax-record/install-record.txt --single-version-externally-managed --compile failed with error code 1 in /tmp/pip_build_root/lxml
Storing debug log for failure in /home/michelle/.pip/pip.log