import numpy as np

from scipy.sparse.csgraph import bellman_ford

from scipy.sparse import csr_matrix

​

arr = np.array([

  [0, -1, 2],

  [1, 0, 0],

  [2, 0, 0]

])

​

newarr = csr_matrix(arr)

​

print(bellman_ford(newarr, return_predecessors=True, indices=0))