1. 筛选小写字母
list_x = ['A', 'a', 'B', 'c', 'f', 'g', 'H']
r = filter(lambda x: True if x >= 'a' else False, list_x)
print(list(r))
2. 筛选大写字母
list_x = ['A', 'a', 'B', 'c', 'f', 'g', 'H']
r = filter(lambda x: True if x < 'a' else False, list_x)
print(list(r))