need help putting this into python

def last_index(xs, key): Search through the list xs for value key; return the non-negative index corresponding to the last occurrence of key. If it's not found, return None. Remember: the rightmost match should be reported when multiple matches are present. o Assumption: xs is a list; xs could be empty. Restriction: You can NOT call.index()or.reverse()-just loop through manually and seek the key. Do NOT modify the incoming list xs. Examples o last index( last-index( last-index( [5.10.15.29.25], 15) [3,4,5,6,4,4,5], 4) [100,105,110], 234) 2 5 # 4 is at indexes 1,4,5 None