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数据类型--字典

2018-06-17 23:52:38来源：未知阅读 ()

字典的概念

字典是存储数据的一种方式，与列表和元祖来说更灵活。
元祖的局限性：值是无序，不可变的
列表的局限性：如果里面想存储一个人的名字对应的值时dy，年龄对应的是30。使用一个列表是不行的如下：

1 >>> t=[name="dy",age=30]
2   File "<stdin>", line 1
3     t=[name="dy",age=30]
4            ^
5 SyntaxError: invalid syntax

View Code

字典的使用方法：

字典是python中唯一的映射类型是无序的（哈希表）

字典对象时可变的（数字，字符串，元祖都是不可变；列表和字典是可变的）。

但是字典的键必须使用不可变对象，并且一个字典中可以使用不同类型的键值。

keys()或者vales()返回键列表或者值列表。

items()返回包含键值对的元祖。

常用操作：

索引
新增
删除
键、值、键值对
循环
长度

常用的字典方法

1、len(),hash() (用于判断某个对象是否可以做一个字典的键，非哈希类型报TypeError)

2、dict.clear()：删除字典中的所有元素。

3、dict.fromkeys(seq,val=None)：以seq中的元素为键创建并返回一个字典，val为指定默认值。

4、dict.get(key,default=None):返回key的value，如果该键不存在返回default指定的值

5、dict.has_key(key)：判断字典中是否存在key，建议使用in或者not in代替。

6、dict.items():返回键值对元祖的列表。

7、dict.keys():返回字典中键的列表。

8、dict.iter*()：interitems()，iterkeys()，itervalues()返回迭代子而不是列表。

9、dict.pop(key[,default]):同get()，区别是若key存在，删除并返回dict[key]，若不存在切default未指定值，抛出KeyError异常。

10、dict.setdefault(key,default=None)：同set(),若key存在则返回其value，若key不存在，则dict[key]=default。

11、dict.update(dict2):将dict2中的键值对添加到字典dict中，如果有重复覆盖，原字典不存在的条目添加进。

12、dict.values()：返回字典中所有值的列表。

13、del dict1['a']删除字典中键值为a的元素。

14、dict1.pop('a')删除并且返回键为'a'的元素。

15、dict1.clear()删除字典所有元素。

16、del dict1删除整个字典。

字典的练习：

 1 arg = {'bakend': "www.oldboy.org",
 2        'record': {'server': '100.1.7.9',
 3                  'weight': 20,
 4                  'maxconn': 30
 5                   }
 6        }
 7 
 8 id_db = {
 9     "name": "u1",
10     "age": 20,
11     "sar": "M",
12     "sal": 1000
13 }
14 
15 dic2 = {
16     "name": "dy",
17     "age": 40,
18 }
19 
20 
21 
22 print(arg)
23 
24 
25 #增加
26 arg['record']['name'] = "127.0.0.1"
27 print('增加：',arg)
28 
29 #修改
30 arg['record']['server'] = "127.0.0.1"
31 arg['record']['weight'] = 10
32 
33 print('修改：',arg)
34 
35 #删除：
36 # arg['record'].pop('name') #删除并且返回键为'name'的元素。
37 # arg.clear()                      #删除字典所有元素。
38 # del id_db                       #删除整个字典。
39 del id_db['sar']                  #删除字典中键值为sar的元素。
40 print('删除：',arg)
41 print('删除：',id_db)
42 
43 
44 
45 #初始化一个新的列表：（尽量不要用，除非只有一层）
46 c = dict.fromkeys([6,7,8],["name",{"alex":"dongye"},444])
47 print(c)
48 c[7][1]["name"] = "user1"
49 print(c)
50 注意有坑，所有的字典元素都会存在一个内存块的指针中。
51 
52 
53 
54 
55 #获取：(没有不会报错，只会返回none)
56 ret = arg.get('record')
57 print('获取（无报错）：',ret)
58 ret1 = id_db.get('A4')
59 print('获取（无报错）：',ret1)
60 
61 
62 #将info1的元素覆盖掉info （存在就覆盖，不存在就更新）
63 id_db.update(dic2)
64 print('存在就覆盖，不存在就更新: ',id_db)
65 
66 
67 #字典里面取值，如果有就返回，如果没有就创建个新的。
68 arg.setdefault('record')
69 print('有就返回，没有就创建', arg)
70 
71 arg.setdefault('owner')
72 print('有就返回，没有就创建', arg)
73 
74 arg.setdefault('pwd',1234)
75 print('有就返回，没有就创建', arg)
76 
77 
78 #for 循环：
79 #打印Key和valus
80 #大数据量的时候这样写：
81 for i in id_db:
82     print(i,id_db[i])
83 
84     
85 #打印key和key下标：
86 for k,v in enumerate(info.keys(),1):
87     print("keys:",k,v)

View Code

字典的源代码：

  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         pass
100 
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         pass
110 
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         pass
114 
115     def viewvalues(self): # real signature unknown; restored from __doc__
116         """ D.viewvalues() -> an object providing a view on D's values """
117         pass
118 
119     def __cmp__(self, y): # real signature unknown; restored from __doc__
120         """ x.__cmp__(y) <==> cmp(x,y) """
121         pass
122 
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 False
126 
127     def __delitem__(self, y): # real signature unknown; restored from __doc__
128         """ x.__delitem__(y) <==> del x[y] """
129         pass
130 
131     def __eq__(self, y): # real signature unknown; restored from __doc__
132         """ x.__eq__(y) <==> x==y """
133         pass
134 
135     def __getattribute__(self, name): # real signature unknown; restored from __doc__
136         """ x.__getattribute__('name') <==> x.name """
137         pass
138 
139     def __getitem__(self, y): # real signature unknown; restored from __doc__
140         """ x.__getitem__(y) <==> x[y] """
141         pass
142 
143     def __ge__(self, y): # real signature unknown; restored from __doc__
144         """ x.__ge__(y) <==> x>=y """
145         pass
146 
147     def __gt__(self, y): # real signature unknown; restored from __doc__
148         """ x.__gt__(y) <==> x>y """
149         pass
150 
151     def __init__(self, seq=None, **kwargs): # known special case of dict.__init__
152         """
153         dict() -> new empty dictionary
154         dict(mapping) -> new dictionary initialized from a mapping object's
155             (key, value) pairs
156         dict(iterable) -> new dictionary initialized as if via:
157             d = {}
158             for k, v in iterable:
159                 d[k] = v
160         dict(**kwargs) -> new dictionary initialized with the name=value pairs
161             in the keyword argument list.  For example:  dict(one=1, two=2)
162         # (copied from class doc)
163         """
164         pass
165 
166     def __iter__(self): # real signature unknown; restored from __doc__
167         """ x.__iter__() <==> iter(x) """
168         pass
169 
170     def __len__(self): # real signature unknown; restored from __doc__
171         """ x.__len__() <==> len(x) """
172         pass
173 
174     def __le__(self, y): # real signature unknown; restored from __doc__
175         """ x.__le__(y) <==> x<=y """
176         pass
177 
178     def __lt__(self, y): # real signature unknown; restored from __doc__
179         """ x.__lt__(y) <==> x<y """
180         pass
181 
182     @staticmethod # known case of __new__
183     def __new__(S, *more): # real signature unknown; restored from __doc__
184         """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
185         pass
186 
187     def __ne__(self, y): # real signature unknown; restored from __doc__
188         """ x.__ne__(y) <==> x!=y """
189         pass
190 
191     def __repr__(self): # real signature unknown; restored from __doc__
192         """ x.__repr__() <==> repr(x) """
193         pass
194 
195     def __setitem__(self, i, y): # real signature unknown; restored from __doc__
196         """ x.__setitem__(i, y) <==> x[i]=y """
197         pass
198 
199     def __sizeof__(self): # real signature unknown; restored from __doc__
200         """ D.__sizeof__() -> size of D in memory, in bytes """
201         pass
202 
203     __hash__ = None
204 
205 dict