I tried to build the docs for v3.4.0b1 following the instructions in the Doc/README.txt. My default python is v3.3. I got the following error message: "Error: Sphinx needs to be executed with Python 2.4 or newer (not 3.0 though)." I wondered what was weird about 3.0 as opposed to later versions that it wouldn't work. Fortunately I had run into other situations where tools expected Python 2 but wouldn't work with Python 3, so after a few minutes of head scratching I tried using Python 2, whi Sphinx needs to be executed with Python 2 (v. 2.4 or newer), not Python 3 so that it makes clear that it requires Python 2 not Python 3 and puts the grammatical emphasis where it belongs. More importantly, perhaps, the Doc README should be changed to state that make must use Python 2.
For 2.7 and 3.3, the error message just needs to be fixed (s/3.0/3.x/); it lives in the sphinx-build.py script somewhere in Doc/. For default, though, since we now rely on an installed version of Sphinx rather than a checked out version, the whole version check needs to be removed and just let Sphinx deal with version checking on its own.
