How do I check if the move is valid or not made by knight and bishop

Complete the following function to validate the move of a given chess piece and return True (boolean) if the move is valid or False(boolean) if the move is invalid. The chessboard is given below for your reference.

Function takes 3 arguments

piece can be a "Knight" or "Bishop"

currentpos(a string) is a combination of row and column it be anything between "a1" to "h8". currentpos represents the cell on the chessboard where the piece is currently located

nextpos(a string) is also a combination of row and column and can also be between from "a1" to "h8". nextpos represents the cell to which the piece is intended to be moved


I have a hard time understanding this question. Can anyone tell me the correct approach for this problem implementing bishop and knight?

def valid_move_or_not(piece,currentpos,nextpos):
    if currentpos == nextpos:
        return False
    if piece == 'Rook':
        return (currentpos[0] == nextpos[0]) or (currentpos[1] == nextpos[1])

if __name__=='__main__':
    #you can run your tests here
    print(valid_move_or_not("Knight","a1","a2"))