a = [1, 2, 4, 3, 56, 32]

sorted(range(len(a)), key=lambda x:a[x])
[0, 1, 3, 2, 5, 4]

a = [1, 2, -4, 3, 56, -32]
sorted(range(len(a)), key=lambda x:a[x])
[5, 2, 0, 1, 3, 4]

[2, 3, 1, 4, 5, 0]