Error in python script

I wrote a python script to make an animation but when I run it I get the error

AttributeError: 'module' object has no attribute 'ion'

Here is the script:

import numpy as np

import pylab as pl

data = np.loadtxt( "random.dat" )

pl.ion()

M = len( data[0] )-1
N = len( data[:,0] )

line , = pl.plot(开发者_如何学Python data[0,1:] , pl.ones( M ) , 'o' )

for i in xrange( 1 , N ):
    line.set_xdata( data[i,1:] )
    pl.title( "t=%.2f" % data[i,0] )
    pl.draw()

print "done"

pl.show()

Try pl.pyplot.ion()

http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.ion