假设一个场景:统计一个列表中每一个数据的数目,要求:尽可能不设定初始值
如果你想不出来,你可以先看看设置初始值的最基本的方法。
[En]
If you can’t figure it out, you can first look at the most basic way to set the initial value.
- 首先需要导入库
from collections import defaultdict
原始方案
user_dict = {}
users = ["bobby1", "bobby2", "bobby3", "bobby4", "bobby4", "bobby2", "bobby2"]
for user in users:
if user not in user_dict:
user_dict[user] = 1
else:
user_dict[user] += 1
print(user_dict)
改进
使用setdefault函数完成
user_dict = {}
users = ["bobby1", "bobby2", "bobby3", "bobby4", "bobby4", "bobby2", "bobby2"]
for user in users:
user_dict.setdefault(user, 0)
user_dict[user] += 1
print(user_dict)
改进的改进
使用collection中的defaultdict方法
default_dict = defaultdict(int)
users = ["bobby1", "bobby2", "bobby3", "bobby4", "bobby4", "bobby2", "bobby2"]
for user in users:
default_dict[user] += 1
print(default_dict)
关于defaultdict方法的补充
在初始化并且设定一些特定值的时候可以用到
def gen_default():
return {
"name": "",
"nums": 0
}
default_dict = defaultdict(gen_default)
print(default_dict["group1"])
- 输出结果
defaultdict(, {'bobby1': 1, 'bobby2': 3, 'bobby3': 1, 'bobby4': 2})
{'name': '', 'nums': 0}
Original: https://blog.51cto.com/coderusher/5639114
Author: Coderusher
Title: python 进阶之collections中的defaultdict
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