numpy.nonzero(a)

Return the indices of the elements that are non-zero.

Returns a tuple of arrays, one for each dimension of a, containing the indices of the non-zero elements in that dimension. The values in aare always tested and returned in row-major, C-style order. The corresponding non-zero  values can be obtained with:

import numpy as np

a = np.eye(3);

print np.nonzero(a)
#(array([0, 1, 2]), array([0, 1, 2]))

print np.transpose(np.nonzero(a))
#[[0 0]
# [1 1]
# [2 2]]

[Python] numpy.nonzero