import numpy as np
import matplotlib.pyplot as plt

fig1 = plt.figure() #Create figure

l, = plt.plot([], [], 'r-') #What is the comma for? Is l some kind of struct/class?
plt.xlim(0, 1)
plt.ylim(0, 1)
plt.xlabel('x')
plt.title('test')

k = 5
xdata=[0.5 for i in range(k+1)]     # Generate a list to hold data
ydata=[j for j in range(k+1)]

while True:
    y = float(raw_input("y val :"))
    xdata.append(y)     # Append new data to list
    k = k + 1       # inc x value
    ydata.append(k)
    l.set_data(xdata,ydata) # update data
    print xdata     # Print for debug perposes
    print ydata
    plt.draw        # These seem to do nothing
    plt.show        # !?