基本数据类型
五、字典
字典（Dictionary）是Python中一种由“键-值”组成的常用数据结构。
1.字典格式
Python中使用一对花括号“｛｝”或者dict()函数来创建字典。
dic = { "one":1, "two":2, "three":3}
2.键的不可变性
我们可以将Python中基本数据类型大致分为两类：
- 不可变类型：数字、字符串、元组
- 可变类型：列表、字典
故列表、字典不能作为字典的键。
3.从属关系的判断
与列表类似，可以用关键字in来判断某个键是否在字典中：
dic = { "one":1, "two":2, "three":3}a = "one" in dicprint(a) #结果为：True 判断某个值是否在字典中需要使用values()函数：
dic = { "one":1, "two":2, "three":3}a = 4 in dic.values()print(a) #结果为：False 4.字典的方法
（1）.get()方法
.get()方法根据键获取值,键不存在时,默认值为None。
dic = { "one":1, "two":2, "three":3}a = dic.get("s")print(a) #结果为：None （2）.pop()方法
.pop()方法删除并返回指定键的值。与列表的.pop()方法不同的是列表根据索引位置删除并返回值，而字典根据键删除并返回值。
dic = { "one":1, "two":2, "three":3}a = dic.pop("one")print(a) #结果为：1print(dic) #结果为：{'two': 2, 'three': 3} （3）.update()方法
.update()方法是更新多个键值对。
dic = { "one":6, "two":2, "three":3}a = { "one":1, "four":4 }dic.update(a)print(dic) #结果为：{'one': 1, 'two': 2, 'three': 3, 'four': 4} （4）.keys()方法
.keys()方法返回一个由所有键组成的列表：
dic = { "one":1, "two":2, "three":3}print(dic.keys()) #结果为：dict_keys(['one', 'two', 'three']) （5）.values方法
.values方法返回一个由所有值组成的列表：
dic = { "one":1, "two":2, "three":3}print(dic.values()) #结果为：dict_values([1, 2, 3]) （6）.items方法
.items方法返回一个由所有键值对元组组成的列表：
dic = { "one":1, "two":2, "three":3}print(dic.items()) #结果为：dict_items([('one', 1), ('two', 2), ('three', 3)]) 字典所有方法归纳：
1 class dict(object): 2 """ 3 dict() -> new empty dictionary 4 dict(mapping) -> new dictionary initialized from a mapping object's 5 (key, value) pairs 6 dict(iterable) -> new dictionary initialized as if via: 7 d = {} 8 for k, v in iterable: 9 d[k] = v 10 dict(**kwargs) -> new dictionary initialized with the name=value pairs 11 in the keyword argument list. For example: dict(one=1, two=2) 12 """ 13 14 def clear(self): # real signature unknown; restored from __doc__ 15 """ 清除内容 """ 16 """ D.clear() -> None. Remove all items from D. """ 17 pass 18 19 def copy(self): # real signature unknown; restored from __doc__ 20 """ 浅拷贝 """ 21 """ D.copy() -> a shallow copy of D """ 22 pass 23 24 @staticmethod # known case 25 def fromkeys(S, v=None): # real signature unknown; restored from __doc__ 26 """ 27 dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v. 28 v defaults to None. 29 """ 30 pass 31 32 def get(self, k, d=None): # real signature unknown; restored from __doc__ 33 """ 根据key获取值，d是默认值 """ 34 """ D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None. """ 35 pass 36 37 def has_key(self, k): # real signature unknown; restored from __doc__ 38 """ 是否有key """ 39 """ D.has_key(k) -> True if D has a key k, else False """ 40 return False 41 42 def items(self): # real signature unknown; restored from __doc__ 43 """ 所有项的列表形式 """ 44 """ D.items() -> list of D's (key, value) pairs, as 2-tuples """ 45 return [] 46 47 def iteritems(self): # real signature unknown; restored from __doc__ 48 """ 项可迭代 """ 49 """ D.iteritems() -> an iterator over the (key, value) items of D """ 50 pass 51 52 def iterkeys(self): # real signature unknown; restored from __doc__ 53 """ key可迭代 """ 54 """ D.iterkeys() -> an iterator over the keys of D """ 55 pass 56 57 def itervalues(self): # real signature unknown; restored from __doc__ 58 """ value可迭代 """ 59 """ D.itervalues() -> an iterator over the values of D """ 60 pass 61 62 def keys(self): # real signature unknown; restored from __doc__ 63 """ 所有的key列表 """ 64 """ D.keys() -> list of D's keys """ 65 return [] 66 67 def pop(self, k, d=None): # real signature unknown; restored from __doc__ 68 """ 获取并在字典中移除 """ 69 """ 70 D.pop(k[,d]) -> v, remove specified key and return the corresponding value. 71 If key is not found, d is returned if given, otherwise KeyError is raised 72 """ 73 pass 74 75 def popitem(self): # real signature unknown; restored from __doc__ 76 """ 获取并在字典中移除 """ 77 """ 78 D.popitem() -> (k, v), remove and return some (key, value) pair as a 79 2-tuple; but raise KeyError if D is empty. 80 """ 81 pass 82 83 def setdefault(self, k, d=None): # real signature unknown; restored from __doc__ 84 """ 如果key不存在，则创建，如果存在，则返回已存在的值且不修改 """ 85 """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """ 86 pass 87 88 def update(self, E=None, **F): # known special case of dict.update 89 """ 更新 90 {'name':'alex', 'age': 18000} 91 [('name','sbsbsb'),] 92 """ 93 """ 94 D.update([E, ]**F) -> None. Update D from dict/iterable E and F. 95 If E present and has a .keys() method, does: for k in E: D[k] = E[k] 96 If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v 97 In either case, this is followed by: for k in F: D[k] = F[k] 98 """ 99 pass100 101 def values(self): # real signature unknown; restored from __doc__102 """ 所有的值 """103 """ D.values() -> list of D's values """104 return []105 106 def viewitems(self): # real signature unknown; restored from __doc__107 """ 所有项，只是将内容保存至view对象中 """108 """ D.viewitems() -> a set-like object providing a view on D's items """109 pass110 111 def viewkeys(self): # real signature unknown; restored from __doc__112 """ D.viewkeys() -> a set-like object providing a view on D's keys """113 pass114 115 def viewvalues(self): # real signature unknown; restored from __doc__116 """ D.viewvalues() -> an object providing a view on D's values """117 pass118 119 def __cmp__(self, y): # real signature unknown; restored from __doc__120 """ x.__cmp__(y) <==> cmp(x,y) """121 pass122 123 def __contains__(self, k): # real signature unknown; restored from __doc__124 """ D.__contains__(k) -> True if D has a key k, else False """125 return False126 127 def __delitem__(self, y): # real signature unknown; restored from __doc__128 """ x.__delitem__(y) <==> del x[y] """129 pass130 131 def __eq__(self, y): # real signature unknown; restored from __doc__132 """ x.__eq__(y) <==> x==y """133 pass134 135 def __getattribute__(self, name): # real signature unknown; restored from __doc__136 """ x.__getattribute__('name') <==> x.name """137 pass138 139 def __getitem__(self, y): # real signature unknown; restored from __doc__140 """ x.__getitem__(y) <==> x[y] """141 pass142 143 def __ge__(self, y): # real signature unknown; restored from __doc__144 """ x.__ge__(y) <==> x>=y """145 pass146 147 def __gt__(self, y): # real signature unknown; restored from __doc__148 """ x.__gt__(y) <==> x>y """149 pass150 151 def __init__(self, seq=None, **kwargs): # known special case of dict.__init__152 """153 dict() -> new empty dictionary154 dict(mapping) -> new dictionary initialized from a mapping object's155 (key, value) pairs156 dict(iterable) -> new dictionary initialized as if via:157 d = {}158 for k, v in iterable:159 d[k] = v160 dict(**kwargs) -> new dictionary initialized with the name=value pairs161 in the keyword argument list. For example: dict(one=1, two=2)162 # (copied from class doc)163 """164 pass165 166 def __iter__(self): # real signature unknown; restored from __doc__167 """ x.__iter__() <==> iter(x) """168 pass169 170 def __len__(self): # real signature unknown; restored from __doc__171 """ x.__len__() <==> len(x) """172 pass173 174 def __le__(self, y): # real signature unknown; restored from __doc__175 """ x.__le__(y) <==> x<=y """176 pass177 178 def __lt__(self, y): # real signature unknown; restored from __doc__179 """ x.__lt__(y) <==> x a new object with type S, a subtype of T """185 pass186 187 def __ne__(self, y): # real signature unknown; restored from __doc__188 """ x.__ne__(y) <==> x!=y """189 pass190 191 def __repr__(self): # real signature unknown; restored from __doc__192 """ x.__repr__() <==> repr(x) """193 pass194 195 def __setitem__(self, i, y): # real signature unknown; restored from __doc__196 """ x.__setitem__(i, y) <==> x[i]=y """197 pass198 199 def __sizeof__(self): # real signature unknown; restored from __doc__200 """ D.__sizeof__() -> size of D in memory, in bytes """201 pass202 203 __hash__ = None204 205 dict