7-python3 from beginner to combat-basic data type (dictionary-dictionary)

Python from the start to the actual combat series--the definition of a directory dictionary

• A dictionary is another variable container model, and can store any type of object, with key-value (Key-value) storage, with extremely fast lookup speed;
  Each key value of the dictionary (key=>value) pairs with a colon (:) split, each pair is separated by a comma (,), and the entire dictionary is included in curly braces ({})

  语法格式：{ key1 : value1, key2 : value2, key3 : value3 ...}users={‘ 张三 ‘ : 18 , ‘ 李四 ‘ : 19 , ‘ 王五 ‘ : 20 , ‘ 赵六 ‘ : 19}

• The key of the dictionary must be unique, and the data type of the value is immutable, but the value can be arbitrary or repetitive;

  # 编号作为键，键唯一，值可变users={ 1 :‘ 张三 ‘  , 2 :‘ 李四 ‘ , 3 :‘ 王五 ‘  , 4 :‘ 张三 ‘ }

Accessing values in the dictionary

• Access the values in the dictionary using the dict[key]

  dict = {‘name‘ : ‘ SiberiaDante ‘ , ‘ age ‘ : 18  , ‘ address‘ : ‘ China ‘}print(dict[‘name‘]  # 结果 ：SiberiaDante

Modify Dictionary

• Modify the values in the dictionary according to the keys in the dictionary

  dict = {‘name‘ : ‘ SiberiaDante ‘ , ‘ age ‘ : 18  , ‘ address‘ : ‘ China ‘}print(dict[‘age‘])  # 输出：18dict [ ‘ age ‘ ] = 20print(dict[‘age‘])  # 输出： 20

• Add a key-value pair to an existing dictionary

  dict = {‘name‘ : ‘SiberiaDante‘ , ‘age‘ : 18  , ‘address‘ : ‘China‘}print(dict) # 结果 ：{‘name‘: ‘SiberiaDante‘, ‘age‘: 18, ‘address‘: ‘China‘}dict[‘language‘]=‘Python‘print(dict) # 结果 ： {‘name‘: ‘SiberiaDante‘, ‘age‘: 18, ‘address‘: ‘China‘,‘language‘:‘Python‘}

Delete Dictionary

• Delete a single element in the dictionary: Dict[key]

  dict = {‘name‘ : ‘SiberiaDante‘ , ‘age‘ : 18  , ‘address‘ : ‘China‘}print(dict) # 结果 ： {‘name‘: ‘SiberiaDante‘, ‘age‘: 18, ‘address‘: ‘China‘}del dict[‘name‘]print(dict) # 结果 ： { ‘age‘: 18, ‘address‘: ‘China‘}

• Delete a dictionary: Del dict

  dict = {‘name‘ : ‘SiberiaDante‘ , ‘age‘ : 18  , ‘address‘ : ‘China‘}del dict

• Empty dictionary: Dict.clear ()

     dict = {‘name‘ : ‘SiberiaDante‘ , ‘age‘ : 18  , ‘address‘ : ‘China‘}   print(dict) # 结果 ： {‘name‘: ‘SiberiaDante‘, ‘age‘: 18, ‘address‘: ‘China‘}   dict.clear()    print(dict)  # 结果：{}

  Dictionary built-in functions & methods

• Function

  len(dict)   计算字典元素个数，即键的总数。 str(dict)   输出字典，以可打印的字符串表示。    type(variable)  返回输入的变量类型，如果变量是字典就返回字典类型。

• Method

  dict.clear() 删除字典内所有元素dict.copy()  返回一个字典的浅复制dict.fromkeys()  创建一个新字典，以序列seq中元素做字典的键，val为字典所有键对应的初始值dict.get(key, default=None)  返回指定键的值，如果值不在字典中返回default值key in dict 如果键在字典dict里返回true，否则返回falsedict.items() 以列表返回可遍历的(键, 值) 元组数组dict.keys()  以列表返回一个字典所有的键dict.setdefault(key, default=None)   和get()类似, 但如果键不存在于字典中，将会添加键并将值设为defaultdict.update(dict2)   把字典dict2的键/值对更新到dict里dict.values()    以列表返回字典中的所有值pop(key[,default])  删除字典给定键 key 所对应的值，返回值为被删除的值。key值必须给出。 否则，返回default值。popitem()   随机返回并删除字典中的一对键和值(一般删除末尾对)。

Dictionary and List comparison

• Compared with list, Dict has the following features:
  • The speed of finding and inserting is very fast and will not slow with the increase of key;
    * Need to occupy a lot of memory, memory waste much;
• Compared to dictionary, the list features:
  • The time to find and insert increases as the element increases;
  • Small footprint, little wasted memory;

7-python3 from beginner to combat-basic data type (dictionary-dictionary)