matplotlib window blocks threa

1import numpy as np
2from matplotlib import pyplot as plt
3
4def main():
5    plt.axis([-50,50,0,10000])
6    plt.ion()
7    plt.show()
8
9    x = np.arange(-50, 51)
10    for pow in range(1,5):   # plot x^1, x^2, ..., x^4
11        y = [Xi**pow for Xi in x]
12        plt.plot(x, y)
13        plt.draw()
14        plt.pause(0.001)
15        input("Press [enter] to continue.")
16
17if __name__ == '__main__':
18    main()