python画圆运用了什么函数

from matplotlib.patches import Ellipse, Circle

import matplotlib.pyplot as plt

def plot_cicle():

    fig = plt.figure()

    ax = fig.add_subplot(111)

    cir1 = Circle(xy = (0.0, 0.0), radius=2, alpha=0.5)

    ax.add_patch(cir1)

    x, y = 0, 0

    ax.plot(x, y, 'ro')

    plt.axis('scaled')

    plt.axis('equal')   #changes limits of x or y axis so that equal increments of x and y have the same length

    plt.show()

plot_cicle()