This gives an implementation of fcntl for non nix users. If you require this within your dependencies, please have it exclude environments with a real and useful fcntl.
If you work for or can help influence Python to provide this out of the box. Please do, the current error sucks!
pip install fcntl- Lewis Cowles - author/maintainer
This is manually tested. It relies on language features only, and no external libraries. It is under 10 lines of code.