How to find indexes of elements from one array in another?

Question

numpy

There is an array numpy.array
a = [1,2,3]
there is an array numpy.array
b = [3,4,5,1,2]
We need to find the indices of elements from a to b , here it is [3, 4, 0]
Those. the operation is the reverse of taking an index on another array b[X] == a
Perhaps there is a way not to go through a in the Python loop using where each time, but to solve everything beautifully with one ready-made method?
All elements of a are guaranteed to occur exactly once in b.