dev-python/thunarx-python-0.3.0-r1 is only compatible with 2.7, per the ebuild. However, the build system pulls 3.3:

checking for python... /usr/bin/python
checking for python version... 3.3
checking for python platform... linux
checking for python script directory... ${prefix}/lib64/python3.3/site-packages
checking for python extension module directory... ${exec_prefix}/lib64/python3.3/site-packages
checking for headers required to compile python extensions... found
checking for libraries required to embed python... yes

It looks like in configure.ac, it's hard-coded to just use /usr/bin/python and python-config to identify how to build against python.