Python的collections之defaultdict的使用及其优势

user_dict = {}
users = ["baoshan1", "baoshan2", "baoshan3","baoshan1", "baoshan2", "baoshan2"]
for user in users:
    if user not in user_dict:
        user_dict[user] = 1
    else:
        user_dict[user] += 1
print(user_dict)

user_dict = {}
users = ["baoshan1", "baoshan2", "baoshan3","baoshan1", "baoshan2", "baoshan2"]
for user in users:
    user_dict.setdefault(user, 0)
    user_dict[user] += 1
print(user_dict)

# 不需要做if else的判断
# 效率高，少一次user_dict的查询操作

from collections import defaultdict
user_dict = defaultdict(int)
users = ["baoshan1", "baoshan2", "baoshan3","baoshan1", "baoshan2", "baoshan2"]
for user in users:
    user_dict[user] += 1
print(user_dict)
# defaultdict的好处，传递可调用的对象例如int、list、函数等