Comments and variables in Python

This is my participation 11 The fourth of the yuegengwen challenge 1 God , Check out the activity details ：2021 One last more challenge

notes

What is annotation

• It won't be in the code Python Directly run statements

Why use notes

• Facilitate the later reading of the code
• Facilitate the later maintenance of the code

Three uses of annotations

#	Single-line comments
''' '''	Multiline comment
""" """	Multiline comment

Python Script execution entry

What is a script entry

• The execution of the program also needs such an entry
• — Generally, we call the entry of code execution as the main function main

How to write code script

If your name is Xiaoming .py, In the eyes of friends , You are Xiaoming (__name_==‘ Xiao Ming ’__);

In your own eyes , You are yourself ( __name_ == '__main_' )

Indent

# coding：utf-8

import os


if __name__ == '__main':
	print(os.getcwd())
print(" I return 1 Level code block ")
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• Indent the same level of proof code

For the code entry, hope is the last of the code

Variable

What is a variable

for instance ：

Prepare a glass , We can pour coke into the glass or sprite into the glass , The glass doesn't change during this process , What changes is the liquid in the glass . Here we can think of the glass as a variable name , Treat the liquid in the glass as a variable value, and this process is assignment .

Pictured ：

summary ： What is a variable

• Assignment statement
• You can change the value by assigning a value to the variable name
• The variable name can remain unchanged , Variable values can be changed
• A variable name with a variable value —— Variable

Where do you live

• Variables exist in the memory of our computer
• Each variable is defined and stored in a memory block

Rules for variable names

• form : It has to be numbers , Letter , Underline composition
• length : Any length , But not too long ,20 Within characters
• requirement : Must start with a letter
• Be careful : Case sensitive 、 meaningful

Common errors about variables

#  The variable name naming rule is wrong, and the error message 
SyntaxError: invalid token
#  Using undefined variables 
NameError: name 'worker' is not defined
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Defining variables

# coding: utf-8

usename = ' Xiaomo '
age = 20
is_sleep = 'ok'
is_eat,is_learn,is_play = 'yes','no','no'
#01work='01'

if __name__ == '__main__':
    print(usename)
    print(age)
    print(is_sleep)
    print(is_eat)
    print(is_learn)
    print(is_play)
    #print(worker)

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Be careful ： If you define multiple variables on the same line , Then the defined variable value must correspond to the variable name one by one , Otherwise, an error will be reported

Error message ：ValueError: not enough values to unpack (expected 3, got 2)