Python variables

• Variables are used to store some intermediate results in the computation of programs. In order to facilitate future calls, variables must be descriptive.

  Variable can be regarded as a container for information, marked and stored in memory, which can be used in the whole program.

    student_number=30
    studentNumber=30 #Hump Microsoft programmers often use

• Naming rules for variables

  To be descriptive
  Variable names cannot be named in Chinese. They can only be numbers, letters, spaces or special characters
  Cannot start with a number
  Cannot use reserved characters
  Cannot start with an uppercase letter

• Constant = = constant quantity

  The constant in python is variable, so the variable name in all uppercase means that the variable is constant.

• Assignment of variables

    name="OurNYeras"  
    name2=name  
    print(name,name2)

• When is the memory freed for recycling?

  Empty automatically when not in use, i.e. when not pointing.

    age=21
    print(age)
    del age #Hard dismantling
  

  When reassigning, the original assignment is invalid. Python memory timing recovery mechanism.

• Encoding (2.x does not support Chinese)

    #!-*- coding:utf-8 -*-  
  
    #coding:utf-8
  

Notes and input / output

• Notes

  Add "×" before the code to represent a single line comment
  Add a comment after the code to comment on the code
  Multiline comments are preceded by three single quotes or three double quotes

• User input

  A program that interacts with a user.

    name=input("your name:")
    age=input("your age:")
    print(name,age)
  

  Enter an age and print how many years you can live.

    #Convert the string to int, and use int (the transferred data)
    #To convert data into strings, use str
    death_age=200
    age=input("your age:")  #All data received by input is "string", even if the input is a number, it will be treated as a string.
    print("you can still live for",death_age-int(age),"years.")  
  

  Guess age

    age_of_men = 56
    guess_age=int(input(">>:"))
    if guess_age==age_of_men:
        print("yes")
    elif guess_age>age_of_men:
        print("try samller.")
    else:
        print("try bigger.")
  

  Grade judgment

    score = int(input("score:"))
    if score > 90:
        print("A")
    elif score > 80:
        print("B")
    elif score > 70:
        print("C")
    elif score > 60:
        print("D")
    elif score < 60:
        print("rolling")
  

  Simple exercises

    # This program says hello and asks for my name.
  
    print("hello world!")
    print("what is your name?") #Ask for the name
    my_name = input()
    print("It is good o meet you,"+my_name)
    print("The length of your name is:")
    print(len(my_name))
    print("What is your age?")  #Ask age
    my_age = input()
    print("you will be"+str(int(my_age)+1)+"in a year.")