Python 基础【第六篇】字典

1.字典定义：

　　字典和列表类似 只是字典标示符用的是字符而列表用的是0开始的数字，字典中每个元素对应一个值 这个元素叫做键（key）键值不能重复 value（值）可以重复

2.字典格式：

格式一：

[Name]={‘key1’:’value1’,’key2’:’value2’,………}

例：

>>>dictionary={'key1':'value1','key2':'value2','key3':'value3'}

>>>print (dictionary)

{'key3': 'value3', 'key2': 'value2', 'key1': 'value1'}

格式二：

[Name]={}

Name[‘key1’]=’value1’

Name[‘key2’]=’value2’

………

例：

>>> dictionary={}

>>> dictionary['key1']='value1'

>>> dictionary['key2']='value2'

>>> dictionary['key3']='value3'

>>> print (dictionary)

{'key3': 'value3', 'key2': 'value2', 'key1': 'value1'}

三、字典的方法

dict.keys() //查看字典中的键

        >>> dictionary.keys()
        ['key3', 'key2', 'key1']

dict.get() //获取字典中指定键的值

        >>> dictionary={'key1':'value1','key2':'value2','key3':'value3'}
        >>> dictionary.get("key1")
        value1

dict.values()  //查看字典中所有的值

        >>> dictionary.values()
        ['value3', 'value2', 'value1']

dict.items() //获取字典中所有键、值 以列表的方式输出 其中对应的键、值通过元组进行组合

        #-*- coding:utf-8 -*-
        #/usr/bin/env python
        >>> dictionary={'key1':'value1','key2':'value2','key3':'value3'}
        >>> dictionary.items()
        [('key3', 'value3'), ('key2', 'value2'), ('key1', 'value1')]

dict.has_key //判断key是否存在如果存在则返回True 否则则返回False

        >>> dictionary={'key1':'value1','key2':'value2','key3':'value3'}
        >>> dictionary.has_key('key1')
        True
        >>> dictionary.has_key('alan')
        False

dict.pop('key') //删除并返回key对应的值

        >>> dictionary={'key1':'value1','key2':'value2','key3':'value3','key4':'value4'}
        >>> dictionary.pop('key1')
        'value1'
        >>> dictionary
        {'key3': 'value3', 'key2': 'value2', 'key4': 'value4'}

dict.popitem() //随机删除并以元组的方式返回字典中的任意一个键值对

        >>> dictionary={'key1':'value1','key2':'value2','key3':'value3','key4':'value5'}
        >>> dictionary.popitem()
        ('key3', 'value3')
        >>> dictionary
        {'key2': 'value2', 'key1': 'value1', 'key4': 'value5'}

dict['key'] = value //如果不存在键值则创建 如果存在则覆盖

        >>> dictionary={'key1':'value1','key2':'value2','key3':'value3','key4':'value4'}
        >>> dictionary['key1']='alan'
        >>> dictionary
        {'key3': 'value3', 'key2': 'value2', 'key1': 'alan', 'key4': 'value4'}

dict.copy() //复制字典 在内存中重新开辟一块空间

        >>> dictionary={'key2': 'value2', 'key4': 'value4'}
        >>> test = dictionary.copy()
        >>> test
        {'key2': 'value2', 'key4': 'value4'}
        #查看test对应的内存地址
        >>> id(test)
        45940000
        #查看dictionary对应的内存地址
        >>> id(dictionary)
        45859440

注:
            如果直接赋值 test = dictionary 那么他们将共享同一份内存数据

            >>> test = dictionary
            >>> id(test)
            45859440
            >>> id(dictionary)
            45859440