Introduction to dictionaries in Python

I've already introduced python String in data type 、 Tuples and lists , Next, we introduce another data type ： Dictionaries .

A dictionary is a kind of disorder (3.6 Order after version ) Object collection for , use {} identification , With key:value In the form of data storage . The elements in the dictionary are through the keys (key) To access , Instead of taking values by index . The elements of the dictionary are key value pairs , key (key) Immutable type must be used , In the same dictionary , key (key) Is the only one. .

Create a dictionary ：

• adopt dict Function to create a dictionary
• {key1：value1,key2：value2,...,key_n：value_n}： Specify specific Dictionary key value pairs , Key value pairs are separated by commas , Finally, enclose it in curly braces .

a = {}
a = {"name":"xiaobo","age":29}
b = dict(a) # {"name":"xiaobo","age":29}
b = dict([("name","xiaobo"),("age",29)]) # {"name":"xiaobo","age":29}

Dictionary data acquisition ：

• adopt get(key) function ：key There is no return None
• adopt dict['key'] obtain ：key There is no error reporting

a = {"name":"xiaobo","age":29}
print(a.get('name'))
print(a.get('name11'))
print(a['name'])
print(a['name1'])

Modify dictionary data ：

update()： When the data does not exist, create , If it exists, it will be updated

 Suppose the dictionary is a = {"name":"xiaobo","age":29},
modify name： a['name']= " Xiaobo "
Use update() Function modification ：
a = {"name":"xiaobo","age":29}
row = {"height":173}
a.update(row)

Delete the dictionary value ：

pop(key) function ： According to one key Delete data , return key Corresponding value, When calling a method , Incoming key There must be , Otherwise, an error will be reported ：

a = {"name":"xiaobo","age":29}
print(a.pop('name')) #xiaobo

popitem() function ： Usually delete the last element , Calling this method with an empty dictionary will report an error

a = {"name":"xiaobo","age":29}
a.popitem() # remove age data , be left over name
a.popitem() # The dictionary becomes empty
a.popitem() # Calling this method with an empty dictionary will report an error 

clear() function ： Empty dictionary .

del Delete some key：

a = {"name":"xiaobo","age":29}
del a["name"]

ACCESS Dictionary View :

• items（）： Returns the view of all key value pairs in the dictionary .
• keys（）： Returns the dictionary key view chart .
• values（）： Returns the dictionary value view .

a = {"name":"xiaobo","age":29}
print(a.items()) # dict_items([('name', 'xiaobo'), ('age', 29)])
print(a.keys()) # dict_keys(['name', 'age'])
print(a.values()) #dict_values(['xiaobo', 29])

Dictionary summary ：