pgadmin4 install problems

First time install from git of pgadmin4, a few problems.
Requirements seem to be installed correctly, but on make I get Babel not
imported. pip shows that Flask  and Babel are in.
I'm getting the impression that python 3 is required, since if I try 2.7
I get many problems with importlib.util not available.
On my system I have both 2.7 and 3.4 installed, "python" calls 2 and
"python3" calls python 3.
If I export PYTHONPATH to the site packages for 3.4 I get a reference in
the error message to "/usr/lib/python2.7/site-packages/flask/exthook.py"
that is the 2.7 version. If I export the 2.7 path I get babel not found.
So I guess I have missed a step which indubitably calls one or other
version of Python?

Error follows:
pgadmin4 # export PYTHONPATH=/usr/lib64/python3.4/site-packages
linux-tqr4:/home/colin/pgadmin4 # make
LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 make -C docs/en_US -f
Makefile.sphinx html
make[1]: Entering directory '/home/colin/pgadmin4/docs/en_US'
Generating code-snippet.rst for some of the important classes...
Traceback (most recent call last):
   File "build_code_snippet.py", line 14, in <module>
     from pgadmin.utils import PgAdminModule
   File "/home/colin/pgadmin4/web/pgadmin/__init__.py", line 14, in <module>
     from flask.ext.babel import Babel
   File "/usr/lib/python2.7/site-packages/flask/exthook.py", line 87, in
load_module
     raise ImportError('No module named %s' % fullname)
ImportError: No module named flask.ext.babel
Makefile.sphinx:20: recipe for target 'code_snippet' failed
make[1]: [code_snippet] Error 1 (ignored)
sphinx-build -b html -d _build/doctrees   . _build/html
Running Sphinx v1.2b3
loading pickled environment... not yet created

Theme error:
no theme named 'sphinx_rtd_theme' found (missing theme.conf?)
Makefile.sphinx:46: recipe for target 'html' failed
make[1]: *** [html] Error 1
make[1]: Leaving directory '/home/colin/pgadmin4/docs/en_US'
Makefile:94: recipe for target 'docs' failed
make: *** [docs] Error 2