Not much to explain, just a test case:
import numpy import rpy2.robjects as rob print numpy.array(rob.FloatVector([1,2,3])) getbuffer main:1: RuntimeWarning: Item size computed from the PEP 3118 buffer format string does not match the actual item size. [ 1. 2. 3.] }}}
Even though it claims the sizes don't match, they in fact do, so it's not a functionality problem, just that the warning message is very annoying. I'm using python 2.7 with rpy2 2.1.7 and numpy 1.5.0.