I installed python3.5.5 from source using make altinstall. Now I also need python3-dev. However I can not find any info on what version I need to work with 3.5.5. If I google python-dev version for Ubuntu 18.04 it always points me to versions in the apt that are labeled 3.6.x but I assume I need a 3.5.x python-dev.
try this one:
sudo add-apt-repository ppa:deadsnakes/ppa sudo apt-get install python3.5-dev
I found this at: Install Tensorflow 1.8.0 with GPU from source on Ubuntu 18.04 Bionic Beaver, hope this work for you :)