When I first done `make` to compile Python 3.9, I did not installed some debian development packages, like `uuid-dev`. So `_uuid` module was not built.

After installed the debian package I re-run `make`, but it failed to build `_uuid` module. I had to edit manually `Modules/_uuidmodule.c` and remove all the `#ifdef` directives and leave only `#include <uuid/uuid.h>`

Maybe `HAVE_UUID_UUID_H` and `HAVE_UUID_H` are created at `configure` phase only?

Is this still a problem after you run configure again?

As pointed out in https://devguide.python.org/setup/#unix

> If you decide to Install dependencies, you will need to re-run both configure and make.

Well, the fact is, basically, for the other libraries you have not to re-run `configure`. You have to install only the missing C libraries and redo `make`. This works, for example, for zlib, lzma, ctypes, sqlite3, readline, bzip2.

Furthermore, it happened to me that I re-run `configure` without a `make clean` before: the `make` process stopped because configuration was changed, and I have to do a `make clean`. A big waste of time.

Sorry about your experience Marco but I think the dev guide is pretty clear on all these steps (including having to redo `make clean`). You can find some discussion on the build system here https://discuss.python.org/t/is-there-prior-discussion-around-the-build-system-of-cpython-itself/2813 but for now I'm going to close this as "not-a-bug" because the dev guide covers it.

If your proposal is to make dependent modules build without re-configuring, please contribute to that discussion or bring it up on the ideas forum.

Ah, well, this is not possible. I was banned from the mailing list. I wrote my "defense" to conduct-wg@python.org in date 2019-12-29, and I'm still waiting for a response...