count列表中字符出现的次数

如何count列表中字符出现的次数？
可以将其生成一个字典。key是列表中的字符串，value是出现的次数

例如
gen = [2, 3, 4, 5, 6, 7, 3, 4, 5, 6, 7, 8, 4, 5, 6, 7, 8, 9, 5, 6, 7, 8, 9, 10, 6, 7, 8, 9, 10, 11, 7, 8, 9, 10, 11, 12]
gen_cnt = {b:gen.count(b) for b in set(gen)}
print(gen_cnt)
{2: 1, 3: 2, 4: 3, 5: 4, 6: 5, 7: 6, 8: 5, 9: 4, 10: 3, 11: 2, 12: 1}