Python learning notes NO.1 variables, comments and simple input and output

Keywords: Python encoding

;

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.")

Posted by karenn1 on Sun, 03 May 2020 17:54:11 -0700