This is a technology preview to allow plugin writers and packagers-installer writers to update their plugins and scripts. This release is not production ready, so use for testing!"
It is recommended to use Gramps 4.0.0 with python 3.2 so as to be ready for the future (python 2.7 works though).
The dependencies for Gramps 4.0.0 are completely different than 3.4 due to the switch to GObject introspection, and the removal of autotools. So only install 4.0.0 if you are certain you can obtain the dependencies, see README and INSTALL.