animation - Plotting animated quivers in Python

Question

I am trying to animate a vector such as wind in Python. I tried to use quiver function in pylab and in combination with matplotlib.animation from matplotlib. However, the result says 'QuiverKey' object is not subscriptable. I think that it is because I don't understand fully about these two functions or just these two functions don't match together. Below is my code, it is actually the combination between quiver and animation functions from matplotlib.

def update_line(num, data, line):
    line.set_data(data[...,:num])
    return line,

X,Y = np.meshgrid(np.arange(0,2*np.pi,.2),np.arange(0,2*np.pi,.2) )  
U = np.cos(X)
V = np.sin(Y)

fig1 = plt.figure()
Q = quiver( X[::3, ::3], Y[::3, ::3], U[::3, ::3], V[::3, ::3],
        pivot='mid', color='r', units='inches' )
data = quiverkey(Q, 0.5, 0.03, 1, r'$1 frac{m}{s}$', fontproperties={'weight': 'bold'})
plt.axis([-1, 7, -1, 7])
title('scales with plot width, not view')
l, = plt.plot([], [], 'r-') 
plt.xlabel('x')
plt.ylabel('y')
plt.title('test')
line_ani = animation.FuncAnimation(fig1, update_line, 25, fargs=(data, l),
interval=50, blit=True)
plt.show() 

Answer 1

Here's an example to get you started:

import numpy as np
from matplotlib import pyplot as plt
from matplotlib import animation

X, Y = np.mgrid[:2*np.pi:10j,:2*np.pi:5j]
U = np.cos(X)
V = np.sin(Y)

fig, ax = plt.subplots(1,1)
Q = ax.quiver(X, Y, U, V, pivot='mid', color='r', units='inches')

ax.set_xlim(-1, 7)
ax.set_ylim(-1, 7)

def update_quiver(num, Q, X, Y):
    """updates the horizontal and vertical vector components by a
    fixed increment on each frame
    """

    U = np.cos(X + num*0.1)
    V = np.sin(Y + num*0.1)

    Q.set_UVC(U,V)

    return Q,

# you need to set blit=False, or the first set of arrows never gets
# cleared on subsequent frames
anim = animation.FuncAnimation(fig, update_quiver, fargs=(Q, X, Y),
                               interval=50, blit=False)
fig.tight_layout()
plt.show()