Basic knowledge of lists

Definition list

namelist = [ ] Define an empty list .
You can add content to the list , And search and output according to the subscript .

Different types of data can be defined in the same list , For example, you can add both integer and string types
You can use type() Function prints out the type of the element .

Traverse the list

The traversal of the list can be done with for loop , It can also be used. while.
In the use of while when , It can be used len() The length of the test list , Then set a variable count to end the loop by increasing itself .
Pay attention to while Add subscript when .

General operation of list

increase

The first way ：append(): Add an element at the end .

The second way ：extend(): You can add the elements in the list to the new list in turn .
In the use of append when , If you want to fill in a list ,append You can only add the whole list to the end as an element , While using extend You can split the list , Add the elements in the list in turn .
Use append Methods ：

Use extend Methods ：

The third method ：insert(): Insert the element into the specified position .
insert（1,3） The first variable represents the subscript , The second variable represents the value to be inserted .

Delete

The first way ：del： Used to delete the value of the specified subscript

The second way ：pop： Pop up the value at the end

The third way ：remove： Delete the data of the specified content .

But when there are multiple identical values in the list ,remove You can only traverse to the first value that matches the deleted content and delete it , The duplicate in the back will not be deleted .

modify

Directly modify the value you want to modify .

check

in perhaps not in Used to check whether the content to be found is in the list .
use if To determine whether the content to be searched is in the list .


It can be used at the same time index（） Find out whether there is a value you need to find in the specified range . When it is found, it will return the subscript of the found value , If it cannot be found, an error will be reported .
Note that the range of variables is left open and right closed , Include the value on the left , Excluding the value on the right .

Count the number of values to be found in the list

Use functions count（）

Sort and invert

The inversion of the list is used reverse, Indicates that the elements in the list are flashed out .
For sorting lists sort（）, Sort the list in ascending order by default , If you need to sort flashbacks , Need to be in sort（） Put reverse=True.

List nesting

You can continue to include the list in the list , And the number of data in each list is not unique .

Example ： Assign offices to teachers

There are three offices , Eight teachers , Eight teachers were randomly assigned to three offices , Finally, print the number of people in each office and the name of the teacher .
Ideas ： You need to generate random numbers 、 Add... To the list .
Name the three offices 0、1、2, Then let the random number from 0、1、2 Randomly generated in . Traverse the teacher list , And combine the read teacher name with the randomly generated number , Insert , It means inserting into an office , Repeat until all teachers are assigned . Then output the distribution of each office through circulation .

import random  # Introduce random numbers 
offices = [[],[],[]]  # Three offices 
teachers = ["A","B","C","D","E","F","G","H"]  # Eight teachers 
for name in teachers:
    index = random.randint(0,2)  #index From 0 To 2 Randomly generated number , Subscript representing the office 
    offices[index].append(name)  # Assign the traversed teachers to the office 
i = 1  # Used to mark which office 
for office in offices:
    print(" The office %d Yes %d Famous teachers "%(i,len(office)))
    for teacher in office:
        print(teacher,end="\t")
    print("\n")
    print("-"*20)
    i += 1

``

practice ： Print product information

products = [[“iphone”,6888],[“MacPro”,14800],[“ millet 6”,2499],[“Coffee”,31],[“Book”,60],[“Nike”,699]], You need to print out the following format ：
----- List of goods -----
0 iphone 6888
1 MacPro 14800
2 millet 6 2499
3 Coffee 31
4 Book 60
5 Nike 699
Record the products added by the user , If input q The exit , Print the information added by the user .

Ideas ： The serial number in front of the commodity corresponds to the subscript of the commodity stored in the list , Double loop access list , You can output the product name and price separately . Don't wrap lines when printing , Put a placeholder directly , Change lines when you read the next item .
When recording user additions , use while The cycle keeps recording , Until user input q Jump out of the loop as the end . When storing items entered by users , Create a new list to store product names , In storage , Only read the product name for storage , The amount of goods is calculated separately . And then when outputting , Read the stored product name and output the total amount .

products = [["iphone",6888],["MacPro",14800],[" millet 6",2499],["Coffee",31],["Book",60],["Nike",699]]
print("-----  List of goods  -----")
i = 0
for product in products:
    print(i,end="\t")
    for information in product:
        print(information,end="\t")
    print("\n")
    i += 1
buylist = []
sum = 0
while 1:
    buy = input(" Please enter the item number to be purchased ( With q ending )：")
    if buy == "q":
        break
    if buy != "q":
        buy = int(buy)
        buylist.append(products[buy][0])  # Only add the product name 
        sum += products[buy][1]  # Only calculate the total amount 
print(" The product you want to buy is ：")
for list in buylist:
    print(list)
print(" The total amount is %d"%sum)