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字典是Python语言中唯一的映射类型。字典对象是可变的，它是一个容器类型，支持异构、任意嵌套。
创建字典
语法：{key1:val1,key2:val2,.....}
dict1 = {} #创建空字典
dict2 = {‘n1‘:‘liush‘,‘n2‘:‘spirit‘,‘n3‘:‘tester‘}
字典常用操作及实例展示
可以使用dir(dict)查看字典支持的操作方法
clear
功能：清空字典所有元素
语法：D.clear() -> None. Remove all items from D
实例展示：
1 >>>D = {‘n1‘:‘liush‘,‘n2‘:‘spirit‘,‘n3‘:‘tester‘} 2 >>>D.clear() 3 >>>print D 4 {}
copy
功能：浅复制字典，只是复制字典的内容
语法：D.copy() -> a shallow copy of D
实例展示：
1 >>>D = {‘n1‘:‘liush‘,‘n2‘:‘spirit‘,‘n3‘:‘tester‘} 2 >>>id(D) 3 140388211911208 4 >>>D1 = D.copy() 5 >>>print D1 6 {‘n1‘: ‘liush‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 7 >>>id(D1) 8 140388110074776
fromkeys
功能：用于创建一个新字典，以序列S中的元素作为字典的键，v为新字典中所有键对应的初始值，默认为none。
语法：dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v.v defaults to None
实例展示：
1 >>>L = [‘spirit‘,‘man‘,‘liush‘] 2 >>>D_L = dict.fromkeys(L) 3 >>>print D_L 4 {‘liush‘: None, ‘spirit‘: None, ‘man‘: None} 5 ######################################################## 6 >>>D_L = dict.fromkeys(L,‘test‘) 7 >>>print D_L 8 {‘liush‘: ‘test‘, ‘spirit‘: ‘test‘, ‘man‘: ‘test‘}
get
功能：获取指定键的值
语法：D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>D1 = D.get(‘n4‘) 3 >>>print D1 4 none #n4不在字典D中，返回默认值none 5 ########################################################## 6 >>>D2 = D.get(‘n4‘,‘check‘) 7 >>>print D2 8 check #n4不在字典D中，返回指定值check 9 ########################################################## 10 >>>D3 = D.get(‘n2‘) 11 >>>print D3 12 spirit #n2在字典D中，返回n2对应的值 13 ########################################################## 14 >>>D4 = D.get(‘n2‘,‘check‘) 15 >>>print D4 16 spirit #n2在字典D中，指定值无效，依然返回其对应值
has_key
功能：判断字典中是否存在指定键
语法：D.has_key(k) -> True if D has a key k, else False
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>D.has_key(‘n4‘) 3 False 4 ###################################################### 5 >>>D.has_key(‘n2‘) 6 True
items
功能：返回以字典中的键值对组成的元组作为元素的列表
语法：D.items() -> list of D‘s (key, value) pairs, as 2-tuples
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>L = D.items() 3 >>>print L 4 [(‘n1‘, ‘liushuai‘), (‘n2‘, ‘spirit‘), (‘n3‘, ‘tester‘)] 5 >>>type(L) 6 <type ‘list‘>
iteritems
功能：对以字典中的键值对组成的元组进行迭代，可用于for循环
语法：D.iteritems() -> an iterator over the (key, value) items of D
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>L = D.iteritems() 3 >>>print L 4 <dictionary-itemiterator object at 0x7faea6c97158> #生成一个迭代器地址 5 >>>L.next() #开始迭代 6 (‘n1‘, ‘liushuai‘) 7 >>>L.next() 8 (‘n2‘, ‘spirit‘) 9 >>>L.next() 10 (‘n3‘, ‘tester‘) 11 >>>L.next() #迭代完成后报错 12 Traceback (most recent call last): 13 File "<stdin>", line 1, in <module> 14 StopIteration 15 ######################################################################### 16 >>>for i in D.iteritems(): #使用for循环遍历 17 ... print i
18 ... 19 (‘n1‘, ‘liushuai‘) 20 (‘n2‘, ‘spirit‘) 21 (‘n3‘, ‘tester‘)
iterkeys
功能：对字典中的键进行迭代(遍历)
语法：D.iterkeys() -> an iterator over the keys of D
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>L = D.itervalues() 3 >>>print L 4 <dictionary-keyiterator object at 0x7faea6c971b0> 5 >>>L.next() 6 ‘n1‘ 7 >>>L.next() 8 ‘n2‘ 9 >>>L.next() 10 ‘n3‘ 11 >>>L.next() 12 Traceback (most recent call last): 13 File "<stdin>", line 1, in <module> 14 StopIteration 15 ############################################################# 16 >>>for i in D.iterkeys(): 17 ... print i 18 ... 19 n1 20 n2 21 n3
itervalues
功能：对字典中的键进行迭代(遍历)
语法：D.itervalues() -> an iterator over the values of D
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>L = D.itervalues() 3 >>>print L 4 <dictionary-valueiterator object at 0x7faea6c97208> 5 >>>L.next() 6 ‘liushuai‘ 7 >>>L.next() 8 ‘spirit‘ 9 >>>L.next() 10 ‘tester‘ 11 >>>L.next() 12 Traceback (most recent call last): 13 File "<stdin>", line 1, in <module> 14 StopIteration 15 ############################################################# 16 >>>for i in D.itervalues(): 17 ... print i 18 ... 19 liushuai 20 spirit 21 tester
keys
功能：以列表的形式返回所有键
语法：D.keys() -> list of D‘s keys
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>L = D.keys() 3 >>>print L 4 [‘n1‘,‘n2‘,‘n3‘]
pop
功能：从字典中删除指定的键，返回其对应的值。
语法：D.pop(k[,d]) -> v, remove specified key and return the corresponding value. If key is not found, d is returned if given, otherwise KeyError is raised
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>D.pop(‘n4‘) #指定的键不存在，返回报错 3 Traceback (most recent call last): 4 File "<stdin>", line 1, in <module> 5 ################################################## 6 KeyError: ‘n4‘ #指定的键不存在，返回指定的值 7 >>>D.pop(‘n4‘,‘check‘) 8 ‘check‘ 9 ################################################## 10 >>>D.pop(‘n2‘) #指定的键存在，返回其对应值 11 ‘spirit‘ 12 ################################################## 13 >>>D.pop(‘n3‘,‘check‘) #指定的键存在，指定值无效，依然返回其对应值 14 ‘tester‘ 15 ##################################################
popitem
功能：随机删除字典的键值对并以元组的形式返回
语法：D.popitem() -> (k, v), remove and return some (key, value) pair as a
2-tuple; but raise KeyError if D is empty.
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>D.popitem() 3 (‘n1‘, ‘liushuai‘) 4 >>>D.popitem() 5 (‘n2‘, ‘spirit‘) 6 >>>D.popitem() 7 (‘n3‘, ‘tester‘) 8 >>>D.popitem() #当字典为空时，抛出异常。 Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: ‘popitem(): dictionary is empty‘
setdefault
功能：查找键值。若键不在字典中，将会添加键并将值设定为默认值
语法：D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 ##指定的键存在，则返回其对应的值，原字典不变 3 >>>D.setdefault(‘n2‘) 4 ‘spirit‘ 5 >>>print D 6 {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 7 ####################################################################### 8 ##指定的键不存在，则修改原字典，该键对应的值默认为none 9 >>>D.setdefault(‘n4‘) 10 >>>print D 11 {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘, ‘n4‘: None} 12 ####################################################################### 13 ##指定的键不存在，则修改原字典，该键对应的值为指定值 14 >>>D.setdefault(‘n5‘,‘check‘) 15 >>>print D 16 {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘, ‘n4‘: None, ‘n5‘: ‘check‘}
update
功能：以字典或迭代器更新原字典
语法： D.update([E, ]**F) -> None. Update D from dict/iterable E and F.
If E present and has a .keys() method, does: for k in E: D[k] = E[k]
If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v
In either case, this is followed by: for k in F: D[k] = F[k]
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>D1 = {‘n1‘:‘liush‘,‘n4‘:‘Jerry‘} 3 >>>D2 = {1:‘IT‘,2:‘SALE‘} 4 #键相同时，则其对应的原字典的值将被覆盖 5 >>>D.update(D1) 6 {‘n1‘: ‘liush‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘, ‘n4‘: ‘Jerry‘} 7 #################################################### 8 #键不同时，则追加 9 >>>D.update(D2) 10 {1: ‘IT‘, 2: ‘SALE‘, ‘n1‘: ‘liush‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘, ‘n4‘: ‘Jerry‘}
values
功能：以列表的形式返回所有值
语法：D.values() -> list of D‘s values
实例展示：
1 >>>D = {‘n1‘: ‘liushuai‘, ‘n2‘: ‘spirit‘, ‘n3‘: ‘tester‘} 2 >>>L = D.values() 3 >>>print L 4 [‘liushuai‘, ‘spirit‘, ‘tester‘]
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原文地址：http://www.cnblogs.com/spiritman/p/5142559.html
