Python之Dict

字典是一种映射类型。映射类型包括对象里的哈希值（键）和指向的对象（值）。

一、字典的创建

创建字典值需要把字典赋值给变量即可。

>>> dic1 = {'k1':'v1','k2':'v2'}
>>> dic1
{'k2': 'v2', 'k1': 'v1'}

方法1

>>> dic2 = dict(k1='v1',k2='v2')
>>> dic2
{'k2': 'v2', 'k1': 'v1'}

方法2

>>> dic3 = {}.fromkeys(('k1','k2'),-1)
>>> dic3
{'k2': -1, 'k1': -1}

方法3

二、字典的一些操作

a.访问

要访问字典中的某个元素的值，可用字典加上中括号‘[]’来得到。

>>> dic2['k1']
'v1'

dic

b.更新

>>> dic2['k1'] = 'v3'
>>> dic2
{'k2': 'v2', 'k1': 'v3'}

update

c.删除

>>> del dic2['k2']
>>> dic2
{'k1': 'v3'}

del

>>> dic2.clear()
>>> dic2
{}

clear

三、内置函数&方法

    def clear(self): 
    #删除字典中所有元素

    def copy(self): 
    #浅copy

    def fromkeys(*args, **kwargs): 
    #创建并返回一个新字典
    dic3 = {}.fromkeys(('k1','k2'),-1)
    >>> dic3

    def get(self, k, d=None): 
    #对字典dict 中的键key,返回它对应的值value

    def items(self): 
    #获取一个包含字典中(键, 值)对元组的列表

    def keys(self): 
    #获取一个包含字典中键的列表

    def pop(self, k, d=None): 
    #和方法get()相似，如果字典中key 键存在，删除并返回dict[key]，如果key 键不存在，且没有给出default 的值

    def popitem(self): 

    def setdefault(self, k, d=None): 
    #字典中不存在key 键，由dict[key]=default 为它赋值
    >>> dic2.setdefault('k4')
    >>> dic2
    {'k4': None}

    def update(self, E=None, **F):
    #将字典的键-值对添加到字典dict
    >>> dic1
    {'k2': 'v2', 'k1': 'v1'}
    >>> dic1.update({'k3':123})
    >>> dic1
    {'k2': 'v2', 'k3': 123, 'k1': 'v1'}

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

    def __contains__(self, *args, **kwargs): # real signature unknown
        """ True if D has a key k, else False. """
        pass

    def __delitem__(self, *args, **kwargs): # real signature unknown
        """ Delete self[key]. """
        pass

    def __eq__(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

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

    def __ge__(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def __gt__(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        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, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def __len__(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def __le__(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def __lt__(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __ne__(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def __setitem__(self, *args, **kwargs): # real signature unknown
        """ Set self[key] to value. """
        pass

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

method&f(x)