Generating numbers with unequal probability

Here is the thing.

I want to generate two values, 1 and -1, with different probability. When I run this script, I get the message " choice() got an unexpected keyword argument 'p'"

Can anyone tell me why this happens and how to fix it? Thanks.

from scipy import *
import matplotlib.pyplot as plt
import random as r

def ruin_demo():


    tmax = 1000       #The number of game rounds
    Xi = 10           #The initial money the gambler has
    T = []
    M = []
    t = 1
    for N in linspace(0.3, 0.49, 100):     #The probability changing region

        meandeltaX = 1.0*N + (1-N)*(-1.0)  #The expected value for each game round
        M.append(meandeltaX)
        while (t < tmax and Xi > 0):

            deltaX  = r.choice((1, -1), p=[N, 1-N]) # The change of money during each game round
                #print deltaX
            Xi = Xi + deltaX
            t = t + 1
        T.append(t)
    plt.plot(M, T)
    plt.show()

ruin_demo()