Python [dictionary]

Python [dictionary]

Dictionaries are another model of mutable containers that can store objects of any type.

Each key-value key->valuepair of a dictionary is separated by a colon, each pair is separated by a comma, and the entire dictionary is enclosed in curly braces, in the following format:

d = {
    
    2:123,1:10}
print(d[2])
print(d[1])
d[2] = 100
print(d[2])

output:

123
10
100

Use built-in functions to create dictionaries:

d = dict()      # 创建字典
print(d)        # 打印字典，此时为空
print(len(d))   # 打印字典的键值对数量
print(type(d))  # 查看d的类型

output:

{}
0
<class 'dict'>

modify, add, delete

d = dict()      # 创建字典
d[1] = 10       # 添加元素
d[2] = 50       # 添加元素
print(d)
d[1] = 20       # 修改元素
print(d)

del d[1]        # 删除键1
print(d)
d.clear()       # 清空字典
print(d)
del d           # 删除字典

output:

{1: 10, 2: 50}
{1: 20, 2: 50}
{2: 50}
{}

Commonly used built-in functions for dictionaries

d = dict()      # 创建字典
d[1] = 10       # 添加元素
d[2] = 50       # 添加元素
print(len(d))   # 查看字典的元素个数
print(1 in d)   # 查看键1是否在d中
print(3 in d)   # 查看键3是否在d中
x = d.copy()    # 将d的内容复制给x
del x[1]        # 对x的操作不会影响d
print(x)
print(d)

output:

2
True
False
{2: 50}
{1: 10, 2: 50}