for i, ((xmu, ymu), (xsigma, ysigma)) in enumerate(zip(centers, sigmas)): code example

Example: enumerate zip python

alist = ['a1', 'a2', 'a3']
blist = ['b1', 'b2', 'b3']

for i, (a, b) in enumerate(zip(alist, blist)):
    print i, a, b