LXML package states, that has minimal requirements on python - Requires: Python >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, != 3.4.* Based on what I see on Travis, it seems to me, that for python 3.9.x. the minimum stable LXML version is 4.3.x; is that expected? Sample log: Collecting lxml==4.2.6 Downloading lxml-4.2.6.tar.gz (2.4 MB) Building wheels for collected packages: lxml Building wheel for lxml (setup.py) ... error ERROR: Command errored out with exit status 1: command: /home/travis/virtualenv/python3.9.1/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-i7un6wlk/lxml_b3782dbd0b1b4611a75033d4ab809f51/setup.py'"'"'; __file__='"'"'/tmp/pip-install-i7un6wlk/lxml_b3782dbd0b1b4611a75033d4ab809f51/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /tmp/pip-wheel-v441aa6c … … creating build/temp.linux-x86_64-3.9/src/lxml gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -g -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security -fPIC -DCYTHON_CLINE_IN_TRACEBACK=0 -I/usr/include/libxml2 -Isrc -Isrc/lxml/includes -I/home/travis/virtualenv/python3.9.1/include -I/opt/python/3.9.1/include/python3.9 -c src/lxml/etree.c -o build/temp.linux-x86_64-3.9/src/lxml/etree.o -w src/lxml/etree.c: In function ‘__Pyx_modinit_type_init_code’: src/lxml/etree.c:230310:32: error: ‘PyTypeObject {aka struct _typeobject}’ has no member named ‘tp_print’ __pyx_type_4lxml_5etree_Error.tp_print = 0; You can see the full logs and which version was installed sucessfully and which not on the compatibility build matrix here: https://app.travis-ci.com/github/SAP/python-pyodata/builds/233333488