This is somewhat related to Bug#818201, in that it
involves that fact that the --build-base option only
appears to be operational under the build command.

Hence it is not possible to do:

python setup.py install -b <somedir>

The --help for install does not say that one can, so
the situation is not as inconsistent as in the previous
bug report. Nevertheless, it is problematic that once
one does:

python setup.py build -b <somedir>

as far as I can tell there is _no way_ to just install
the result.

One needs to always do:

python setup.py build -b <somedir> install

This seems somewhat unwieldy; perhaps -b should be
more universally available to all distutil commands?

Thanks for the report. distutils does not get new features anymore. This gives us time to focus on distutils2, the next generation. Thanks to the configure command (#8254), the functionality you require will be easily supported in distutils2. I’ll get back to this feature when configure is 100% finished and merged into the main repo.

Actually I think this bug can be fixed in distutils.

I’ve found a distutils commit that shows that this option was removed on purpose, because people might except that using “install -b foo” would affect the build command, but it does not.  I don’t think it’s a problem.  For people who run build and install in separate steps, it should be possible to say “build -b spam” and then “install -b spam”.