Python 數據類型之字典

Python 數據類型之字典

鍵值對的無序集合
鍵和值必須成對出現
只能通過鍵獲取值

創建字典
    創建字典和創建集合類似
    應當指定鍵值對而不是值
        >>> a_dict = {'Name':'Sam','Age':20}
        >>> a_dict
        {'Name': 'Sam', 'Age': 20}
        >>> a_dict['Name'] =  'zhang'
        >>> a_dict
        {'Name': 'zhang', 'Age': 20}
        >>> a_dict['Age']
        20
修改字典
    字典內不允許有重複的鍵
    鍵值區分大小寫
    對既有字典賦值只能新值替代舊值
        >>> a_dict
        {'Name': 'zhang', 'Age': 20}
        >>> a_dict['age'] = 30
        >>> a_dict
        {'Name': 'zhang', 'Age': 20, 'age': 30}
        >>> a_dict['age'] = 28
        >>> a_dict
        {'Name': 'zhang', 'Age': 20, 'age': 28}
混合值字典
    字典的值可以是任何數據類型那個
    in 判斷鍵是否在字典中存在
        >>> a_dict = {'old':[1,2,3],'new':[4,5,6]}
        >>> a_dict['old']
        [1, 2, 3]
        >>> a_dict['old'][2]
        3
        >>> 'new' in a_dict
        True
布爾上下文環境中的字典
    空字典爲假，非空字典爲真