Analysis of flask source code (I) request entry

Flask Source analysis

flask It's based on Python Developed wsgi Micro frame .flask There are two core dependency Libraries ：Werkzug and jinjia. among werkzeug Responsible for the core logic module , Like routing 、 Encapsulation of requests and responses 、WSGI Related functions, etc ;jinja Responsible for rendering templates , It's mainly used to render the html The contents of the document .

1. entrance

web Programs are from the server through related wsgi In the relevant program of conversion ,Django This method has been used in ,Django 3.x And later versions have added ASGI Processing requests asynchronously .

flask What's used internally in is Werkzug Processing performed by the module .

1.1 Werkzug Introduction and use of

werkzueg Is an excellent tool library , Use werkzueg To achieve a fit WSGI Agreed web Applications

Supplement of object-oriented knowledge :

class Base:
    def __call__(self, *args, **kwargs):
        print("call  Yes ")
    def func(self):
        print("func ...")

obj = Base()
# obj()
obj.func()

Easy to use

from werkzeug import run_simple

def func(environ,start_response):
    #  To change the function, you need to write these two parameters , Because these two values are needed inside the source code 
    print(" The request came. ")

if __name__ == '__main__':
    # app.run()
    run_simple("127.0.0.1",5000,func)
>>>  Click request address ( When the request comes in )
>>>  The request came. 
>>>  Report errors 
#  The function is executed as  func()

From the above example, we can see , When you click request address ( When the request comes in ), adopt werkzug Started a small web Program , And execute related functions . When we try to change functions into classes .

from werkzeug import run_simple

class FlaskBase:
    def __call__(self, *args, **kwargs):
        print("call Method executed ")

app = FlaskBase()

if __name__ == '__main__':
    # app.run()
    run_simple("127.0.0.1",5000,app)
>>>  Click request address  
>>> call  The method is implemented 
>>  Report errors 

Particular attention ： When you click request address ( When the request comes in ), Through this, you can find that the object is passed into , It's equivalent to executing object (), Therefore, the incoming and outgoing values go back to the corresponding implementation class __call__ Method .

werkzug start-up flask

from flask import Flask
from werkzeug import run_simple

app = Flask(__name__)

if __name__ == '__main__':
    run_simple("127.0.0.1",5000,app)

• werkzug You can put a small flask The application starts directly .

1.2 ordinary Flask Website

#  The simplest  flask  application 
from flask import Flask

app = Flask(__name__)

if __name__ == '__main__':
    app.run()

flask During the startup of run() Method .

# Flask Internal source code ：run Part of the source code inside the method 
from werkzeug.serving import run_simple

try:
    run_simple(t.cast(str, host), port, self, **options)
    #  There are mainly three parameters passed here ： Address 、 Port number 、 object .
    #  In particular ： The object here is an object that has been instantiated outside , namely  app
    #  According to the above research , When the request comes in , Will execute flask  Of __call__ Method .
finally:
    # reset the first request information if the development server
    # reset normally. This makes it possible to restart the server
    # without reloader and that stuff from an interactive shell.
    self._got_first_request = False

flask Inside __call__() Method

def __call__(self, environ: dict, start_response: t.Callable) -> t.Any:
    """The WSGI server calls the Flask application object as the WSGI application. This calls :meth:`wsgi_app`, which can be wrapped to apply middleware. """
    #  Here you will see that the function also has these two parameters  environ,start_response
    return self.wsgi_app(environ, start_response)

• Through the internal method of the source code, we can see ,Flask The essence of startup is still Werkzug.run_simple() function , Conduct web The start of the program .

Conclusion ：

• flask from werkzug To start the , In essence, what is carried out is Werkzug.run_simple() function .
• important ：flask in , When the request comes , The execution is object __call__() Method

Although the rain is wide , Not moist and rootless . Learning is difficult , Diligence can reach its peak ;