Attribute key error

I have installed Gnuradio-3.1.3 on Red Hat Enterprise Linux-4.The
installation of gnuradio was successful.Even I have got USRP connected
and have loaded the firmware.

But when I try to run the given examples of “gr-utils” for example
usrp_fft.py i get the following error:-

[root@localhost python]# ./usrp_fft.py Traceback (most recent call
last):

File “./usrp_fft.py”, line 23, in ?

from gnuradio import gr, gru

File “/usr/lib/python2.3/site-packages/gnuradio/gru/init.py”, line 37,
in ?

exec “from gnuradio.gruimpl.%s import *” % (f,)

File “”, line 1, in ? File
“/usr/lib/python2.3/site-packages/gnuradio/gruimpl/gnuplot_freqz.py”,
line 28, in ?

import numpy

File “/usr/lib/python2.3/site-packages/numpy/init.py”, line 107, in ?

import ma

File “/usr/lib/python2.3/site-packages/numpy/ma/init.py”, line 14, in ?

import core

File “/usr/lib/python2.3/site-packages/numpy/ma/core.py”, line 114, in ?

max_filler.update([(k,-numpy.inf) for k in [numpy.float32,
numpy.float64]])

AttributeError?: keys

What is the reason for such type of error.Can someone guide me through
this problem.

Thanks.