Retrun event.xdata from a function - python-2.7

Question

I have made a small gui to select points on a given image, plot the points, interpolate them and save them. I would like to make it so that the interpolated points are given as output of the function gui_pos(image) retrun, but I couldn't find the way to do it. So far I have fixed it saving the interpolated point in a .pckl file but it is not a good solution.
The code is the following:
from PIL import Image
import numpy as np
import pickle
import matplotlib.pyplot as plt
from scipy.interpolate import interp1d
def interp_mia(x,y,xx):
f= interp1d(x,y,fill_value="extrapolate")
yy= f(xx)
return yy
def onclick(event):
plt.plot(event.xdata, event.ydata, '.')
fig.canvas.draw()
coordsx.append(event.xdata)
coordsy.append(event.ydata)
if (event.button == 3) :
xx = np.arange(np.min(coordsx),np.max(coordsx))
yy = interp_mia(coordsx, coordsy, xx)
print('you pressed', event.button)
plt.plot(xx,yy,'k-')
fig.canvas.draw()
fig.canvas.mpl_disconnect(cid)
dum = np.array((xx,yy))
f = open('gui_pos.pckl', 'wb')
pickle.dump(dum, f)
f.close()
def gui_pos(image):
global coordsx
global coordsy
global fig
global cid
global xx
global yy
global slit
fig = plt.figure()
ax = fig.add_subplot(111)
ax.imshow(image, origin="lower")
coordsx = []
coordsy = []
cid = fig.canvas.mpl_connect('button_press_event', onclick)
return
Any ideas?
Thank you,
Qarolina