Python字典的基础知识

1.注意事项:

1.key(键)，必须唯一，value(值)，可以重复
2.字典是无序的

2.查字典中的值：

d={1:"one",2:"two",3:"three",4:"four"}
print(d[2])

	输出结果：two

3.增加数组中的值：

d={1:"one",2:"two",3:"three",4:"four"}
d[5]="a"
print(d)

	输出结果：d={1:"one",2:"two",3:"three",4:"four",5:"a"}

4.删除字典中的值：—直接报错

d={1:"one",2:"two",3:"three",4:"four"}
del d
print(d)

	输出结果：Traceback (most recent call last):
			  File "E:/python/wenjie/笔记/字典.py", line 14, in <module>
	 		   print(d)
			NameError: name 'd' is not defined

5.删除字典中的值：—标准删除

d={1:"one",2:"two",3:"three",4:"four"}
a=d.pop(2)
print(d)
print(a)

	输出结果：d={1:"one",3:"three",4:"four"}
			two

6.删除字典中的值：—随机删除

d={1:"one",2:"two",3:"three",4:"four"}
d.popitem() 
print(d)

	输出结果：随机删除其中一个

7.查找字典中的值：

d={1:"one",2:"two",3:"three",4:"four"}
print(d.get(3))
print(4 in d)   #判断d中是否存在该键值

	输出结果：three
		 true

8.打印字典中的所有值：

d={1:"one",2:"two",3:"three",4:"four"}
print(d.values())

	输出结果：dict_values(['three', 'two', 'four', 'one'])

9.打印字典中的所有键：

d={1:"one",2:"two",3:"three",4:"four"}
print(d.keys())

	输出结果：dict_keys([3, 2, 4, 1])

10.字典拼接：

d={1:"one",2:"two",3:"three",4:"four"}
d2={5:"three",6:"two",7:"four"}
d.update(d2)
print(d)

	输出结果：
	d={1:"one",2:"two",3:"three",4:"four",5:"three",6:"two",7:"four"}

11.打印所有项：

d={1:"one",2:"two",3:"three",4:"four"}
print(d.items())

	输出结果：dict_items([(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')])

12.字典初始化：

c=dict.fromkeys([1,2,3],"Python")
print(c)

	输出结果：{1: 'Python', 2: 'Python', 3: 'Python'}

fromkeys现象说明

c=dict.fromkeys([1,2,3],[1,{"a":"A"},"Python"])
print(c)
c[3][1]["a"]="AAA"
print(c)

	输出结果：
{1: [1, {'a': 'A'}, 'Python'], 2: [1, {'a': 'A'}, 'Python'], 3: [1, {'a': 'A'}, 'Python']}
{1: [1, {'a': 'AAA'}, 'Python'], 2: [1, {'a': 'AAA'}, 'Python'], 3: [1, {'a': 'AAA'}, 'Python']}

Python字典的基础知识

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