x1 = mu + sigma * P.randn(7000)
x2 = mu + sigma * P.randn(3000)
w0 = np.ones_like(x0)
w0[:len(x0) / 2] = 0.5
w1 = np.ones_like(x1)
w1[:len(x1) / 2] = 0.5
w2 = np.ones_like(x2)
w0[:len(x2) / 2] = 0.5
P.figure()
n, bins, patches = P.hist([x0, x1, x2], 10, weights=[w0, w1, w2], histtype=
    'bar')
P.show()
how can I plot 4 histograms on the same graph