Content summary

• Basic use of pychar
• Annotation syntax
• Variables and constants
• Garbage collection mechanism
• data type

Detailed content

Note that the Python environment should be downloaded locally, and the main.py script file is not checked temporarily

Topic selection:

pycharm switch interpreter:

Click add

Select the desired interpreter and click OK

How to create a Python script file

Right click the folder where you selected to store the project

Just enter a name and press enter

Since the suffix of the file is used to identify the data characteristics inside the file, our Python file also has a unique suffix. py

How to adjust font size

Check and click OK

Then when writing code, you can press Ctrl to slide the pulley on the mouse to zoom in and out

How to run Py files

Right click in the file content area and select run

Python annotation syntax (comments are the mother of code!!!)

What is a comment

​ A comment is an explanation of a piece of code

How to use annotations

​ Method 1: use '#' single line annotation

​ Method 2: use three quotation marks (either single or double) to comment on multiple lines

pycharm annotation shortcut

				Ctrl + ？

Note:

​ # There must be a space between and the comment text

​ If a single line comment follows a line of code, you need to leave two spaces blank before writing

​ pycharm also provides automated format code functionality

Python code writing specification: PEP8 specification

Want to quickly grasp the automatic tips with pycharm, compare before and after, and memorize every day

variable

What are variables

	That is, the amount of change is used to record a certain state of things (imitating the memory ability of human things)

How to use variables

	In daily life:

			full name: zhangsan

			Age: 18

			Hobbies: Music

	In the program:

			username = 'zhangsan'

			age = 18

			hobby = 'music'

	Syntax format:

			username  =  'zhangsan'

			Variable name assignment symbol variable value
"""
Underlying principle (must know!!)
		In case of assignment symbols, first look to the right of the symbols and then to the left:  age = 18
		
		1.Apply for a memory space storage 18 in the memory space
		2.Bind the memory space address of 18 to the variable name age
		3.Then, if you want to access 18, you can use the variable name age Just visit
"""

Naming conventions and styles

# Naming conventions
	Variable names can only be any combination of numbers, letters and underscores
    	user@name(incorrect), _(sure),pwd_123_aaa(sure)
	Variable names cannot start with numbers. It is recommended not to start with underscores because they have special meanings
 	Variable names cannot conflict with keywords:
    	For example: name = print
    Variable names must be named according to the name (important)
    """Variable name is the core, no matter how long the variable is"""
# Naming style
	1.Hump body
    	Big hump  # All words are capitalized
        	UserNameFromDb
         Small hump  # The first letter is lowercase and the rest is uppercase
        	userNameFromDb
    '''JavaScript Hump body is recommended'''
	2.Underline # Words are separated by underscores
    		user_name_from_db
        '''python Underline is recommended'''

constant

# It is mainly used to record some unchanged states

# In Python, there is no constant in the real sense, and we regard all uppercase variables as constants
		HOST = '127.0.0.1' # Generally, it is used more in the configuration file
# In other programming languages, the definition of constants in the real sense cannot be modified
		const pi = 3.14 # Define constants
    	 pi = 4 # Modification is not supported

Three elements of variables

1.Value of variable
2.Memory address of variable
3.Data type of variable

name = 'zhangsan'
print(name) # value
print(id(name)) # A string of numbers corresponds to the memory address number
print(type(name)) # Data type < class' STR '>

Python underlying optimization

When the amount of data is very small, if multiple variable names need to be used, they will point to the same address
"""
A variable name can only point to one memory address
 A memory address can have multiple variable names pointing to
"""

Garbage collection mechanism

# Definition of garbage data
	There is no data in memory that the variable name points to
    
#  An automatic recycling scheme is developed for garbage data
	1.Reference count
    	There are several variable names on the variable value in memory, and the binding count is just a few. As long as it is not 0, it is not garbage
	2.Mark clear
    	When the memory is about to fill up  Python It will automatically pause the execution of the program and scan the data in memory from beginning to end
        After marking, the marked data is cleared at one time
	3.Generation recycling
    	The supervision of data will be divided into three levels, and the supervision frequency will decrease with the decrease of the level

data type

# What is a data type?
	In real life, there are many ways and manifestations of storing data
    	File text table file video file audio file picture file...
	stay IT The storage methods and forms of data in the world are also changeable

Integer int of data type

# Understanding: integer int
 Function: record the age of the person and the number of classes...
definition:
    	age = 18 # Writing an integer directly is an integer

Floating point float of data type

# Understanding: decimal float
 Function: record people's weight, salary and height
 definition:
	salary = 3.1 # Writing decimals directly is floating point

"""
Integer and floating point types can be collectively referred to as numeric types
 It is mainly used for mathematical operation and comparison operation
"""