Python --字典
類似其他的hash，關聯數組，key-value，key不可變。
創建字典
方法1：dict1 = {1:'one',2:'two',3,"three"}
dict1 = {} //空字典
方法2: dict(mapping) -> new dictionary initialized from a mapping object's (key, value) pairs
t1 = ((1,'one'),(2,'two')) #元組不可變類型
dict2 = dict(t1) #工廠函數
dict2 = dict()
訪問字典
通過key訪問value
one = dict1[1] # 1 是 key
方法
1.D.clear() 與 D = {} 的區別? #D爲字典
>>> dict1 = {1:'one',2:"two",3:"three"}
>>> dict2 = dict1 #賦值是將dict2這個引用指向dict1指向的字典
>>> hex(id(dict1))
'0x25149b56f48'
>>> hex(id(dict2))
'0x25149b56f48'
>>> dict1 = {}
>>> dict1
{}
>>> dict2
{1: 'one', 2: 'two', 3: 'three'}
>>> hex(id(dict1)) # 創建了一個新的空字典
'0x25149bc5ec8'
>>> hex(id(dict2))
'0x25149b56f48'
>>> dict1 = dict2
>>> dict1.clear() #與dict1的引用指向相同的都置空
>>> dict1
{}
>>> dict2
{}
>>> hex(id(dict1))
'0x25149b56f48'
>>> hex(id(dict2))
'0x25149b56f48'
2.D.copy()
>>> dict1 = {1:'one',2:'two'}
>>> dict2 = dict1.copy() #淺拷貝
>>> hex(id(dict1))
'0x25149bc6748'
>>> hex(id(dict2))
'0x25149bc5ec8'
淺拷貝(shallow copy) VS 深拷貝(deep copy) 在copy
compound objects (objects that contain other objects, like lists or class instances) 時有區別
>>> import copy
>>> a = [1,2,3]
>>> b = [4,5,6]
>>> c = [a,b]
#普通的賦值
>>> d = c
>>> print(id(c) == id(d))
True
>>> print(id(c[0]) == id(d[0])
)
True
#淺拷貝
sd = copy.copy(c)
>>> print(id(sd) == id(c))
False
>>> print(id(sd[0]) == id(c[0])) #引用的拷貝
True
#深拷貝
>>> dd = copy.deepcopy(c)
>>> print(id(dd)==id(c))
False
>>> print(id(dd[0]) == id(c[0])) #新建的對象
False
參考鏈接
1.http://stackoverflow.com/questions/17246693/what-exactly-is-the-difference-between-shallow-copy-deepcopy-and-normal-assignm
2http://www.jianshu.com/p/efa9dd51f5cc