字典有关

笔记：

1、字典是Python中唯一的映射类型
2、字典包含两个要素：键（key）和值（value）他们是成对出现的，用大括号括起来，多对存在时用逗号隔开。
3、改变字典中的某个值：dict2[key] = ‘value’，插入的方法类似

一、使用dict()函数创建字典
第一种：创建空字典

>>> dict1=dict()
>>> dict1
{}

第二种：关键字参数
dict2 = dict(key1 = value1,key2 = value2)，则最后的形式为：
dict2 = {key2:value2,key1:value1}Python的dict是无序的。

>>> dict2 = dict(one = 1,two = 2,three = 3)
>>> dict2
{'one': 1, 'two': 2, 'three': 3}

!!!!!!!!!!!!!注意以下方法会出错：

>>> dic2 = dict(1 = "one",2 = "two",3 = "three")
SyntaxError: invalid syntax

第三种：dict(list)

>>> list1 = [(1,"one"),(2,"two"),(3,"three")]
>>> dict3 = dict(list1)
>>> dict3
{1: 'one', 2: 'two', 3: 'three'}

第四种：dict(tuple)

可以用dict()直接创建字典，如dict1 = dict(((‘F’,70),(‘i’,105),(’s’,115),(‘h’,104),(‘C’,67)))，创建出来的字典dict1的形式为{(‘F’,70),(‘i’,105),(’s’,115),(‘h’,104),(‘C’,67)}

>>> tup = ((1,"one"),(2,"two"),(3,"three"))
>>> dict4 = dict(tup)
>>> dict4
{1: 'one', 2: 'two', 3: 'three'}

第五种：dict(zip())

>>> t = zip([1,2,3,],[4,5,6,])
>>> t
<zip object at 0x0000000002FD4788>
>>> list(t)
[(1, 4), (2, 5), (3, 6)]
>>> dict5 = dict(t)
>>> dict5
{}
>>> dict5 = dict(zip([1,2,3,],[4,5,6,]))
>>> dict5
{1: 4, 2: 5, 3: 6}

第六种：dict.fromkeys( list , var )
注意第二个参数var，只能是一个变量

>>> dict.fromkeys(range(3),9)
{0: 9, 1: 9, 2: 9}

>>> dict.fromkeys(range(1,3),["one","two",])
{1: ['one', 'two'], 2: ['one', 'two']}

注意zip()函数：

>>> t = zip([1,2,3,],[4,5,6,])
>>> t
<zip object at 0x0000000002FD4788>
>>> list(t)
[(1, 4), (2, 5), (3, 6)]

二、一些常用方法
0. keys() \ values()\items()
略

1.copy()

>>> d = dict(zip([1,2,3],["one","two","three"]))
>>> d
{1: 'one', 2: 'two', 3: 'three'}
>>> temp1 = d.copy()
>>> temp1
{1: 'one', 2: 'two', 3: 'three'}
>>> temp2 = d
>>> temp2
{1: 'one', 2: 'two', 3: 'three'}
>>> id(d)
50135256
>>> id(temp1)
50212656
>>> id(temp2)
50135256

2.clear()

>>> d = dict(zip([1,2,3],["one","two","three"]))
>>> d
{1: 'one', 2: 'two', 3: 'three'}
>>> temp1 = d.copy()

>>> temp2 = d

>>> temp2.clear()
>>> temp2
{}
>>> temp1
{1: 'one', 2: 'two', 3: 'three'}

3.get(key)———->value

>>> d
{1: 'one', 2: 'two', 3: 'three'}
>>> d.get(2)
'two'

4.pop(key)

>>> d.pop(2)
'two'
>>> d
{1: 'one', 3: 'three'}

5.popitem()

>>> d
{1: 'one', 3: 'three'}
>>> d.popitem()
(3, 'three')

6.update()

>>> d
{1: 'one', 3: 'three'}
>>> d.popitem()
(3, 'three')
>>> c = {2:"two"}
>>> d.update(c)
>>> d
{1: 'one', 2: 'two'}