from collections import defaultdict
from functools import reduce
a = ["8A", "4R", "2A", "3H", "7R"]
x = [str(v) + k for k, v in reduce(lambda acc, v: acc.update({v[0]: acc[v[0]] + v[1]}) or acc,
((i[-1], int(i[:-1])) for i in a),
defaultdict(int)).items()]