BUCK (https://facebook.github.io/buck/) is an opensource and extensible build system developed by Facebook based heavily on the build system used at Google. It's DSL is Python and as such one can extend it using just python.
Currently they offer some rudimentary (non documented) support for Python, however that is far from being production ready.
I propose hacking a set of build rules for the Python community.
py_library: this would correspond to a single module, a package, or a set of packages.
py_test: test that automatically sets the environment, virtual env, etc.
py_binary: this is one of the main problems, as there is no standard way to generate a standalone package executable, atlhough there are some alternatives like http://www.pyinstaller.org/, or one could think on building their own exploiting the fact that python can execute zipped files.
py_pypi: generate a pypi package