Get started quickly with flask (I) understand the framework flask, project structure and development environment

Quick start Flask( One ) Understanding framework Flask、 Project structure 、 development environment

Web Develop lightweight frameworks Flask

github: https://github.com/pallets/flask
Official website ： https://flask.palletsprojects.com/en/2.1.x/
Official documents ：https://flask.net.cn/installation.html#installation

Python The most famous frames are Django, Besides, there are Flask、Tornado Other framework . although Flask Not the most famous frame , however Flask It should be one of the most flexible frameworks , This is also Flask The reason why developers like it .

Flask It's a comparison with Django For lightweight Web frame .

Flask Itself is equivalent to a kernel , Almost all other functions need to be extended （ Mail extension Flask-Mail, User authentication Flask-Login）, All need to be implemented with third-party extensions . Its WSGI The tool box uses Werkzeug（ Routing module ）, The template engine uses Jinja2. These two are also Flask The core of the framework .

Extended list ：http://flask.pocoo.org/extensions/

Flask is a web framework for Python, based on the Werkzeug toolkit.

Flash History and team

flask Born in 2010 April Fool's Day , Originally, it was just a small toy written by the author inadvertently , Unexpectedly, it has quietly become popular . The long 8 Year time ,flask No serious official version has been released , But it can't stop it from becoming github The most acclaimed Python Web frame .

flask The kernel has built-in two most important components , All other components are integrated through an extensible plug-in system . The two built-in components are werkzeug and jinja2.

Pallets project

official ：https://palletsprojects.com/

The Pallets Projects are a collection of Python web development libraries that are associated with the Flask microframework as originally developed by Armin Ronacher. Today the Pallets Projects are a community-driven organization with the goal to maintain and improve these libraries.

Pallets The project is Python Web A collection of development libraries , These libraries and Armin Ronacher Originally developed Flask Frame related . Now ,Pallets The project is a community driven organization , The goal is to maintain and improve these libraries .

Pocoo The members of the team are from Python Community , Unify with Pocoo In the name of participating in multiple Python Library and application development . The team consists of Georg Brandl and Armin Ronacher Leader .

Pocoo The team has developed many popular projects , These include ：

• Flask Micro network development framework
• Jinja2 template engine
• Pygments Syntax highlight package
• Sphinx Document processor
• Werzeug WSGI Toolset

flask Operation process

django And flask It's all implemented WSGI agreement
flask With werkzeug Come on wsgi It was packaged ,werkzeug Yes, it is run_simple(‘localhost’, 4000, hello) The first is ip, The second is the project startup port , The third is the executable object , When requested wsgi, The third parameter will be called

Web The server will hand over all requests from the client to Flask Program instance .
Program instance use Werkzeug To do routing distribution （URL Correspondence between request and view function ）.
According to each URL request , Find the specific view function and call it .
Flask After calling the view function , You can return two types of content ：

• String content ： Take the return value of the view function as the content of the response , Return to the client ( browser ).
• HTML Template content ： After getting the data , Put data in HTML In the template file , The template engine is responsible for rendering HTTP The response data , Then return the response data to the client ( browser ).

Use flask Scene

It's mainly for requirements, simple , Small applications with short project cycles .Flask The introduction is very simple , And can be extended to add other functions .

Use PyCharm Quickly create one Flask project

How to use PyCharm Quickly create one Flask project
Reference resources URL: https://blog.csdn.net/xili1342/article/details/125610684

1） Create a new Flask project
File–>New Project choice flask：

The created folder automatically contains the following ：
At the beginning Flask There are many configuration values and conventions with reasonable defaults . By convention , Templates and static files are stored in the application Python In the subdirectory of the source tree , The names are templates and static .
static Catalog ： Static files
templates Catalog ： Templates
venv Catalog ： fictitious Python Environmental Science , Use... In a virtual environment pip The installed packages will be installed into the current virtual environment
app.py file ：

A minimal application app.py

from flask import Flask

# Flask The function takes a parameter name, It will point to the module where the program is located 
app = Flask(__name__)

# The purpose of the decorator is to map routes to view functions 
@app.route('/')
def hello_world():
    return 'Hello World!'


if __name__ == '__main__':
    # Flask Of the application instance run Method start up WEB The server 
    app.run()

1. First we import Flask class . Examples of this class will become our WSGI application .

2. Then we create an instance of this class . The first parameter is the name of the application module or package . If you use The first mock exam （ Like this example ）, Then you should use name , Because the name will be based on this Whether a module is used as an application or imported as a module changes （ May be ‘main’ , It could also be the name of the actual import ）. This parameter is required , such Flask To know where to Find templates, static files, etc . More details can be found in Flask file .

3. And then we use route() Decorator to tell Flask Trigger function URL .

4. Function names are used to generate associated URL . The function finally returns the information that needs to be displayed in the user's browser .

2） Project start

Pycharm Click on run function

Use the command line to run app.py

python app.py

Use flask The command runs
Now by setting the environment variable FLASK_APP=app.py To indicate which application is going to run , And then run flask run To start the application .

flask run

Appoint IP And port :

flask run --host=0.0.0.0 --port= 8001

or ：

flask run -h 0.0.0.0 -p 8001