How can I fix my python code to draw the graph?

My code exits with code 0, so my code has no errors, but it's still running without drawing the flow on the cylinder I want, can anyone help me with this?

    import sympy as s
    import matplotlib.pyplot as plt
    import numpy as np

    from sympy.abc import x,y


    def cylinder_stream_fct(U=1,R=1):
        r=s.sqrt(x**2+y**2)
        theta=s.atan2(y,x)
        return U*(r-R**2/r)*s.sin(theta)
    def velocity_field(psi):
        u=s.lambdify((x,y), psi.diff(y), 'numpy')
        v=s.lambdify((x,y), -psi.diff(x), 'numpy')
        return u,v
    def plot_streamlines(ax, u, v,xlim=(-1,1), ylim=(-1,1)):
        x0, x1=xlim
        y0, y1=ylim
        Y,X= np.ogrid[y0:y1:100j,x0:x1:100j]
        ax.streamplot(X,Y,u(X,Y),v(X,Y),color='red')
    def format_axes(ax):
        ax.set_aspect('equal')
        ax.figure.subplots_adjust(bottom=0, top=1, left=0, right=1)
        ax.xaxis.set_ticks([])
        ax.yaxis.set_ticks([])
        for spine in ax.spines.values():
            spine.set_visible(False)
    psi=cylinder_stream_fct()
    u,v=velocity_field(psi)
    xlim=ylim=(-3,3)
    fig, ax=plt.subplots(figsize=(4, 4))
    plot_streamlines(ax, u, v, xlim, ylim)
    c=plt.Circle((0,0), radius=1,facecolor='none')
    ax.add_patch(c)

    format_axes(ax)