How can I get the index in a series?

Question

I have the data series including these labels for my dataset:

s=['A','A','A','A','B','B','B','B','C','C','C','C','D','D','D','D','D']

I would like to know how can I get the index of first element B and the last element of C.

Answer 1

Index of the first element B

s.index('B')

Index of the last element C

len(s) - s[::-1].index('C') - 1