import numpy as np

from scipy.sparse.csgraph import csgraph_from_dense

​

G2_data = np.array([

    [np.inf, 2, 0],

    [2, np.inf, np.inf],

    [0, np.inf, np.inf]

])

G2_sparse = csgraph_from_dense(G2_data, null_value=np.inf)

print(G2_sparse.data)