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字典的内建方法:
1. fromkeys ()
>>> dict1.fromkeys((1,2,3))
{1: None, 2: None, 3: None}
>>>dict1.fromkeys((1,2,3),'number')
{1: 'number', 2: 'number', 3: 'number'}
>>> dict1.fromkeys((1,2,3),('one','two','three'))
{1: ('one', 'two', 'three'), 2: ('one','two', 'three'), 3: ('one', 'two', 'three')}
2. 访问字典的方法:
(1)keys:
>>> dict1 =dict1.fromkeys(range(5),'赞')
>>> dict1
{0: '赞', 1: '赞', 2: '赞', 3: '赞', 4: '赞'}
>>> for eachkey in dict1.keys():
print(eachkey)
0
1
2
3
4
(2) values:
>>> for eachvalue indict1.values():
print(eachvalue)
赞
赞
赞
赞
赞
(3) items ()
>>> for eachitem in dict1.items():
print(eachitem)
(0,'赞')
(1, '赞')
(2, '赞')
(3, '赞')
(4, '赞')
如果不知道字典中是否有此值,可以用in 或者 not in。
>>> 4 in dict1
True
>>> 5 in dict1
False
当数据规模很大的时候,字典和序列查找的效率有较大差别,字典高效。在字典里查找的是键,而在序列里查找的是元素的值而不是元素的索引号。
(4). 清空字典 clear ( )
>>> dict1
{0: '赞', 1: '赞', 2: '赞', 3: '赞', 4: '赞'}
>>> dict1.clear()
>>> dict1
{}
(5). Copy()
>>> a ={1:'one',2:'two',3:'three'}
>>> b = a.copy()
>>> c = a
>>> c
{1: 'one', 2: 'two', 3: 'three'}
>>> b
{1: 'one', 2: 'two', 3: 'three'}
>>> id(a) # a和c地址一样。
55314824
>>> id(b) #a和b地址一样
55415880
>>> id(c)
55314824
(6) pop ( )
>>> a.pop(2)
'two'
>>> a
{1: 'one', 3: 'three'}
>>> a.popitem() #随机弹出字典元素
(1, 'one')
(7) setdefault ( ):
>>> a ={1:'one',2:'two',3:'three'}
>>> a
{1: 'one', 2: 'two', 3: 'three'}
>>> a.setdefault(4,'小白')
'小白'
>>> a
{1: 'one', 2: 'two', 3: 'three', 4: '小白'}
(8) update ( )
>>> b = {'小白':'狗'}
>>> a.update(b)
>>> a
{1: 'one', 2: 'two', 3: 'three', 4: '小白', '小白': '狗'}
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