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)