1. Note the file path
I put the files on disk D, as shown below; You can set it according to your own situation
2. The python environment should be downloaded locally
As shown below:
Click the existing environment of the machine. If NO interpr is prompted, click step 2
If not, continue as shown in the figure below
Topic selection
Click file, settings, - Editor - color - scheme
As shown in the figure below:
pycharm switch interpreter
Click file settings Project Python Interpreter
As shown in the figure below:
How to create a python script file
Because the suffix of the file is used to identify the internal data characteristics of the file, our python file also has a unique suffix . py
How to adjust font size
Open file---settings---Editor---general --- and check change font size with ctrl mouse wheel
How to run py files
Right click in the file content area and select run.... py
Annotation syntax of python
"" "comments are the mother of code!!!" "" 1. What are comments? Comments are the interpretation of a piece of code. They do not participate in the operation of the program, but only serve as a reminder. "
2. How to use annotation method 1 use alarm # single line annotation method 2 use three quotation marks (single and double) multi line annotation
3.pycharm annotation shortcut key ctrl +?
"" "1. There must be a space between the alarm number and the comment text."
2. If a single line comment follows a line of code, you need to leave two blank before writing. pycharm also provides the function of automatic format code ctrl+alt+l code reformat code ""“
python code writing specification > > >: pep8 specification # how to quickly master the automatic prompt with the help of pycharm, compare it before and after, and memorize it every day
variable
variable
### # 1. What are variables
That is, the amount of change is used to record a certain state of things(Ability to imitate human memory)
### # 2. How to use variables
In daily life:
full name:Jason
Age:18
hobby:study
In the program:
username = 'jason'
age = 18
hobby = 'music'
"""
Syntax format
username = 'jason'
Variable name assignment symbol variable value
Underlying principle(Will!!!)
In case of assignment symbol, first look at the one on the right and then the one on 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
1.Variable names can only be any combination of numbers, letters and underscores
user@name(incorrect),_(sure),pwd_123_aaa(sure)
2.Variable names cannot start with numbers. It is recommended not to start with underscores because they have special meanings
3.Variable names cannot conflict with keywords
4.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
stay python There is no constant in the real sense. 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, there are constants in the real sense, which cannot be modified once they are defined
const pi = 3.14 # Define constants
pi = 4 # Modification is not supportedThree elements of variables
1. Value of variable
2. Memory address of variable
3. Data type of variable
Examples
name = 'jason'
print(name) # value
print(id(name)) # a string of numbers is equivalent to the memory address number
print(type(name)) # data type < class' STR '>
python underlying optimization
When the amount of value data is very small, if multiple variable names need to be used, they will point to the same block of 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: as shown in the figure below, see
A set of automatic recycling scheme for garbage data python is developed
1. Reference count
There are several variable names on the variable value in memory, and the binding reference count is just a few. As long as it is not 0, it is not garbage
For example, two variables x = 10 and y = 20 are explained in detail as shown in the figure below,
When we execute x=y, the stack area and heap area in memory change as follows
2. Mark clearing --- when the memory is about to be full, python will automatically pause the execution of the program and scan the data in the memory from beginning to end
After marking, the marked data is cleared at one time
3. Generation by generation recycling - the supervision of data will be divided into three levels, and the frequency of supervision will decrease as the level decreases
data type
# What is a data type?
In real life, there are many ways and manifestations of storing data
Text file 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 of Vernacular: integer int
effect: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 of Vernacular: decimal float
effect:Record the person's weight, salary and height
definition:
salary = 3.1 # Writing decimals directly is floating point
Small summary
Integer and floating point types can be collectively referred to as numeric types It is mainly used for mathematical operation and comparison operation