数据类型--字典

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：

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

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：

arg = {'bakend': "www.oldboy.org",
       'record': {'server': '100.1.7.9',
                 'weight': 20,
                 'maxconn': 30
                  }
       }

id_db = {
    "name": "u1",
    "age": 20,
    "sar": "M",
    "sal": 1000
}

dic2 = {
    "name": "dy",
    "age": 40,
}



print(arg)


#增加
arg['record']['name'] = "127.0.0.1"
print('增加：',arg)

#修改
arg['record']['server'] = "127.0.0.1"
arg['record']['weight'] = 10

print('修改：',arg)

#删除：
# arg['record'].pop('name') #删除并且返回键为'name'的元素。
# arg.clear()                      #删除字典所有元素。
# del id_db                       #删除整个字典。
del id_db['sar']                  #删除字典中键值为sar的元素。
print('删除：',arg)
print('删除：',id_db)



#初始化一个新的列表：（尽量不要用，除非只有一层）
c = dict.fromkeys([6,7,8],["name",{"alex":"dongye"},444])
print(c)
c[7][1]["name"] = "user1"
print(c)
注意有坑，所有的字典元素都会存在一个内存块的指针中。




#获取：(没有不会报错，只会返回none)
ret = arg.get('record')
print('获取（无报错）：',ret)
ret1 = id_db.get('A4')
print('获取（无报错）：',ret1)


#将info1的元素覆盖掉info （存在就覆盖，不存在就更新）
id_db.update(dic2)
print('存在就覆盖，不存在就更新: ',id_db)


#字典里面取值，如果有就返回，如果没有就创建个新的。
arg.setdefault('record')
print('有就返回，没有就创建', arg)

arg.setdefault('owner')
print('有就返回，没有就创建', arg)

arg.setdefault('pwd',1234)
print('有就返回，没有就创建', arg)


#for 循环：
#打印Key和valus
#大数据量的时候这样写：
for i in id_db:
    print(i,id_db[i])

    
#打印key和key下标：
for k,v in enumerate(info.keys(),1):
    print("keys:",k,v)

字典的源代码：

class dict(object):
    """
    dict() -> new empty dictionary
    dict(mapping) -> new dictionary initialized from a mapping object's
        (key, value) pairs
    dict(iterable) -> new dictionary initialized as if via:
        d = {}
        for k, v in iterable:
            d[k] = v
    dict(**kwargs) -> new dictionary initialized with the name=value pairs
        in the keyword argument list.  For example:  dict(one=1, two=2)
    """

    def clear(self): # real signature unknown; restored from __doc__
        """ 清除内容 """
        """ D.clear() -> None.  Remove all items from D. """
        pass

    def copy(self): # real signature unknown; restored from __doc__
        """ 浅拷贝 """
        """ D.copy() -> a shallow copy of D """
        pass

    @staticmethod # known case
    def fromkeys(S, v=None): # real signature unknown; restored from __doc__
        """
        dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v.
        v defaults to None.
        """
        pass

    def get(self, k, d=None): # real signature unknown; restored from __doc__
        """ 根据key获取值，d是默认值 """
        """ D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None. """
        pass

    def has_key(self, k): # real signature unknown; restored from __doc__
        """ 是否有key """
        """ D.has_key(k) -> True if D has a key k, else False """
        return False

    def items(self): # real signature unknown; restored from __doc__
        """ 所有项的列表形式 """
        """ D.items() -> list of D's (key, value) pairs, as 2-tuples """
        return []

    def iteritems(self): # real signature unknown; restored from __doc__
        """ 项可迭代 """
        """ D.iteritems() -> an iterator over the (key, value) items of D """
        pass

    def iterkeys(self): # real signature unknown; restored from __doc__
        """ key可迭代 """
        """ D.iterkeys() -> an iterator over the keys of D """
        pass

    def itervalues(self): # real signature unknown; restored from __doc__
        """ value可迭代 """
        """ D.itervalues() -> an iterator over the values of D """
        pass

    def keys(self): # real signature unknown; restored from __doc__
        """ 所有的key列表 """
        """ D.keys() -> list of D's keys """
        return []

    def pop(self, k, d=None): # real signature unknown; restored from __doc__
        """ 获取并在字典中移除 """
        """
        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
        """
        pass

    def popitem(self): # real signature unknown; restored from __doc__
        """ 获取并在字典中移除 """
        """
        D.popitem() -> (k, v), remove and return some (key, value) pair as a
        2-tuple; but raise KeyError if D is empty.
        """
        pass

    def setdefault(self, k, d=None): # real signature unknown; restored from __doc__
        """ 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 """
        """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """
        pass

    def update(self, E=None, **F): # known special case of dict.update
        """ 更新
            {'name':'alex', 'age': 18000}
            [('name','sbsbsb'),]
        """
        """
        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]
        """
        pass

    def values(self): # real signature unknown; restored from __doc__
        """ 所有的值 """
        """ D.values() -> list of D's values """
        return []

    def viewitems(self): # real signature unknown; restored from __doc__
        """ 所有项，只是将内容保存至view对象中 """
        """ D.viewitems() -> a set-like object providing a view on D's items """
        pass

    def viewkeys(self): # real signature unknown; restored from __doc__
        """ D.viewkeys() -> a set-like object providing a view on D's keys """
        pass

    def viewvalues(self): # real signature unknown; restored from __doc__
        """ D.viewvalues() -> an object providing a view on D's values """
        pass

    def __cmp__(self, y): # real signature unknown; restored from __doc__
        """ x.__cmp__(y) <==> cmp(x,y) """
        pass

    def __contains__(self, k): # real signature unknown; restored from __doc__
        """ D.__contains__(k) -> True if D has a key k, else False """
        return False

    def __delitem__(self, y): # real signature unknown; restored from __doc__
        """ x.__delitem__(y) <==> del x[y] """
        pass

    def __eq__(self, y): # real signature unknown; restored from __doc__
        """ x.__eq__(y) <==> x==y """
        pass

    def __getattribute__(self, name): # real signature unknown; restored from __doc__
        """ x.__getattribute__('name') <==> x.name """
        pass

    def __getitem__(self, y): # real signature unknown; restored from __doc__
        """ x.__getitem__(y) <==> x[y] """
        pass

    def __ge__(self, y): # real signature unknown; restored from __doc__
        """ x.__ge__(y) <==> x>=y """
        pass

    def __gt__(self, y): # real signature unknown; restored from __doc__
        """ x.__gt__(y) <==> x>y """
        pass

    def __init__(self, seq=None, **kwargs): # known special case of dict.__init__
        """
        dict() -> new empty dictionary
        dict(mapping) -> new dictionary initialized from a mapping object's
            (key, value) pairs
        dict(iterable) -> new dictionary initialized as if via:
            d = {}
            for k, v in iterable:
                d[k] = v
        dict(**kwargs) -> new dictionary initialized with the name=value pairs
            in the keyword argument list.  For example:  dict(one=1, two=2)
        # (copied from class doc)
        """
        pass

    def __iter__(self): # real signature unknown; restored from __doc__
        """ x.__iter__() <==> iter(x) """
        pass

    def __len__(self): # real signature unknown; restored from __doc__
        """ x.__len__() <==> len(x) """
        pass

    def __le__(self, y): # real signature unknown; restored from __doc__
        """ x.__le__(y) <==> x<=y """
        pass

    def __lt__(self, y): # real signature unknown; restored from __doc__
        """ x.__lt__(y) <==> x<y """
        pass

    @staticmethod # known case of __new__
    def __new__(S, *more): # real signature unknown; restored from __doc__
        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
        pass

    def __ne__(self, y): # real signature unknown; restored from __doc__
        """ x.__ne__(y) <==> x!=y """
        pass

    def __repr__(self): # real signature unknown; restored from __doc__
        """ x.__repr__() <==> repr(x) """
        pass

    def __setitem__(self, i, y): # real signature unknown; restored from __doc__
        """ x.__setitem__(i, y) <==> x[i]=y """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """ D.__sizeof__() -> size of D in memory, in bytes """
        pass

    __hash__ = None

dict