list_plot_semilogy not working

edit

import numpy
import matplotlib.pyplot as plt
noise=numpy.random.randn(1,10)
signal = numpy.ones(10) 
snrdb = numpy.arange(10.)
#print snrdb
import mpmath
ber = []
for i in range(0,10):
   ber.append(n(0.5*mpmath.erfc(float(snrdb[i])/sqrt(2))))

list_plot_semilogy(zip(snrdb,ber))

Running the above code with list_plot works but the semilogy option yields an empty graph. Please resolve this. Thanks in advance.