alist = [[1,2,3], [4,5,6], [7,8,9]] blist = [['a','b','c'], ['d','e','f'], ['g','h','i']] item = 1 z = [(i, x.index(item)) for i, x in enumerate(alist) if item in x][0] alist[z[0]][z[1]] = blist[z[0]][z[1]] print alist