import rpy2
from rpy2.robjects import r

print dir(r)

Traceback (most recent call last):
  File "c:rtest.py", line 2, in <module>
    from rpy2.robjects import r
  File "C:Python27libsite-packagesrpy2robjects__init__.py", line 18, in <module>
    from rpy2.robjects.robject import RObjectMixin, RObject
  File "C:Python27libsite-packagesrpy2robjectsrobject.py", line 5, in <module>
    rpy2.rinterface.initr()
RuntimeError: R_USER not defined.