In looking through the setup.py file for uvloop, I see that they purposely do not call super().initialize_options() or super().finalize_options() in their code if they've already been called once.

I think that is why their code is revealing this problem - the 2nd command to be run is inheriting the self.compiler value from the first command since build_ext.initialize_options() isn't being called to (re)set self.compiler to be None.

I'm not sure if there's a "rule" that says each command must call initialize_options() to "sanitize" the object or not but that does explain why the 2nd command is seeing a CCompiler object() for self.compiler on the 2nd time through.