Python创建和访问字典

发布时间：2019-06-28 17:40:52编辑：auto阅读（1770）

    >>> dict1 = {'a':'1','b':'2','c':'3','d':'4'}

    >>> print('a的值是:',dict1['a'])

    a的值是: 1


    >>> dict4 = dict('我' = '快乐', 你 = '伤悲')

    SyntaxError: keyword can't be an expression


    >>> dict4['你'] = '改变悲伤'

    >>> dict4

    {'我': '快乐', '你': '改变悲伤'}


    >>> dict4['他'] = '多加一个'

    >>> dict4

    {'我': '快乐', '你': '改变悲伤', '他': '多加一个'}


    fromkeys(S[,v])    创建并返回一个新的字典

    >>> dict1 = {}

    >>> dict1.fromkeys((1,2,3))

    {1: None, 2: None, 3: None}


    >>> dict1.fromkeys((1,2,3),'num')

    {1: 'num', 2: 'num', 3: 'num'}


    >>> dict1.fromkeys((1,3),'数字')    #如果想用fromkeys修改键的值，不会成功会创建新的字典

    {1: '数字', 3: '数字'}


    访问字典的方法

    keys()

    values()

    items()


    >>> dict2 = {}

    >>> dict2 = dict2.fromkeys(range(2),'列子')

    >>> dict2

    {0: '列子', 1: '列子'}

    >>> for eachkey in dict2.keys():    #values为'列子'    

    print(eachkey)

    0

    1


    >>> for eachitem in dict2.items():

    print(eachitem)

    (0, '列子')

    (1, '列子')

     

    get() 查找方法

    >>> dict2 = dict2.fromkeys(range(10),'列子')

    >>> dict2

    {0: '列子', 1: '列子', 2: '列子', 3: '列子', 4: '列子', 5: '列子', 6: '列子', 7: '列子', 8: '列子', 9: '列子'}

    >>> dict2.get(5,'无')        #如果有则返回值，如果没有则返回'无'

    '列子'

    >>> dict2.get(10,'无')

    '无'


    >>> 5 in dict2     #成员操作符判定  

    True

    >>> 10 in dict2

    False


    clean(）     清空一个字典

    >>> dict2.fromkeys(range(1),'快乐')

    {0: '快乐'}

    >>> dict2.clear()

    >>> dict2

    {}


    copy()

    >>> a = {1:'one',2:'two',3:'three',4:'four'}

    >>> a

    {1: 'one', 2: 'two', 3: 'three', 4: 'four'}

    >>> b = a.copy()

    >>> c = a

    >>> b

    {1: 'one', 2: 'two', 3: 'three', 4: 'four'}

    >>> c

    {1: 'one', 2: 'two', 3: 'three', 4: 'four'}

    >>> 

    >>> c[5] = 'five'

    >>> c

    {1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five'}

    >>> a

    {1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five'}

    >>> b

    {1: 'one', 2: 'two', 3: 'three', 4: 'four'}


    pop()

    popitem() 随机弹出

    >>> a.pop(2)

    'two'

    >>> a

    {1: 'one', 3: 'three', 4: 'four', 5: 'five'}


    >>> a.popitem()

    (5, 'five')

    >>> a

    {1: 'one', 3: 'three', 4: 'four'}


    >>> a.setdefault(7,'seven')

    'seven'

    >>> a

    {1: 'one', 3: 'three', 4: 'four', 7: 'seven'}

    >>> b = {7:'SEVEN'}

    >>> a

    {1: 'one', 3: 'three', 4: 'four', 7: 'seven'}

    >>> a.update(b)

    >>> a

    {1: 'one', 3: 'three', 4: 'four', 7: 'SEVEN'}








关键字：

上一篇： 【PYTHON模块】：协程与greenl

下一篇： python_os_sys学习笔记