Hello and thanks for the report.

> We need build_ext before build_py. Otherwise, when 2to3 is called (in build_py),
> it will not find ext modules,
Why is 2to3 interested in extension modules?  2to3 converts Python code, extension modules are written in C or C++.

> thinking that those modules are global
I don’t understand what you mean.

Can you give me a Python or shell script to reproduce the error or a full description of what you did, what you expected and what went wrong?