n, radii = 50, [.7, .95]
theta = np.linspace(0, 2*np.pi, n, endpoint=True)
xs = np.outer(radii, np.cos(theta))
ys = np.outer(radii, np.sin(theta))

# Insert nan between two closed lines.
xs = np.r_[xs[0,:], np.array([np.nan]), xs[1,:][::-1]]
ys = np.r_[ys[0,:], np.array([np.nan]), ys[1,:][::-1]]

ax = plt.subplot(111, aspect='equal')
ax.fill(np.ravel(xs), np.ravel(ys))
plt.show()