[flask advanced] deeply understand the endpoint of flask routing from the source code

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Preface

A lot of people flask There is a wrong understanding of the routing mechanism , In this section, I will analyze the source code , Take you to know more about flask The routing mechanism of .

flask Route analysis

There are many people to our flask Have a wrong understanding , Think our url Directly corresponding to the view function , There really seems to be no problem on the surface , But you just ignored our endpoint！
Logically speaking , We know url after , There is no problem directly corresponding to our view function , This is positive , Then we reverse the view function to our url It's not very convenient , therefore , our endpoint Can play a reverse construction url The role of .

url_for And endpoint Reverse build url

Let me say something about endpoint How to reverse build URL Of , Actually this endpoint and url_for Is closely linked ,url_for Just reverse construction URL Of .

as follows ：

from flask import Flask,url_for

app = Flask(__name__)

@app.route('/', endpoint='my_index')
def index():
　　return 'index page'

@app.route('/hello')
def hello():
　　return url_for('.my_index', _external=True)

app.run(debug=True)

notes ：
1. stay url_for In reverse , Accept one endpoint Or the function name is parameter ( If it is endpoint,endpoint You need to add a dot in front ), Return the corresponding url Address ( See the source code ).

2. If you use url_for When , Also need to add some , Such as ：{ { url_for(‘.my_index’) }}.

3._external=True If set to True, Then generate an absolute path URL, Pictured above .

Reverse construction is mentioned here by the way , Now let's get back to the point , Look at the following two pieces of code ：

from flask import Flask

app = Flask(__name__)

# @app.route('/user')
# Our decorators also have endpoint Parameters , Under normal circumstances, we omit , If omitted, the default value is function name 
@app.route("/user",endpoint="user") 
def user():
    return "a niu"

app.run(debug=True)

Our decorators also have endpoint Parameters , Under normal circumstances, we omit , If omitted, the default value is function name .

Let's look at the following code ：

from flask import Flask

app = Flask(__name__)

# @app.route("/user",endpoint="user")
def user():
    return "a niu"

app.add_url_rule(rule="/user",endpoint="user",view_func=user)

app.run(debug=True)

Still no problem , thus it can be seen @app.route() and app.add_url_rule() It is equivalent. , In fact, this is what happened at the bottom of the decorator .

add_url_rule() This method has four parameters ：
1.rule： This parameter is very simple , Is the matching routing address
2.endpoint： This parameter is what I want to focus on today ,endpoint.
3.view_func： This parameter is the view function we wrote
4.**options: Variable number of parameters

app.add_url_rule(rule="/user",endpoint="user",view_func=user,methods=['GET'])

Then let's Start with the decorator Go and have a look at the source code , There is a better way to look at the source code is breakpoint debugging , You can try , We can enter flask Inside , Line by line ！

Break the decorator , Right click to start debugging , Then move the mouse to route Click on , then ctrl + B Enter our source code

We can see that the bottom layer of the decorator is indeed add_url_rule, there self We can see from the following variables , It's ours app object .

Then click the above image several times to enter , We will see the part in the above figure that I have framed in red , We can see that this part of the code is right endpoint Judge whether it is empty , If it's empty endpoint Is the view function name .

We continue to step into

We can see that our rule Added to the url_map in .

And then you can see , Save our view function in views_functions In the dictionary , Each key happens to be endpoint, It just forms a mapping .

Then we point the cursor to this line , Click Run below to the cursor , At this point, the operation we want to study is over .

Then click on it self, find url_map, Look at the end url_map What's in it ？

You can see url_map It's a list , Deposit is rule-endpoint mapping , And above we also analyzed endpoint and view_func mapping , It's a dictionary .

Here we can print our url_map and view_functions Come and have a clear look ：

from flask import Flask

app = Flask(__name__)

# @app.route('/user')
#  Our decorators also have endpoint Parameters , Under normal circumstances, we omit , If omitted, the default value is function name 
@app.route("/user",endpoint="user")
def user():
    return "a niu"

if __name__ == '__main__':
    print(app.url_map)
    print(app.view_functions)
    app.run()

It's the same as looking at the source code analysis ！

summary

• Every application app There is one. view_functions, This is a dictionary , Storage endpoint-view_func Key value pair .add_url_rule The first function of is to view_functions To add a key-value pair ( This is in the application run It was done before )

• Every application app There is one. url_map, It's a Map class ( The concrete realization is werkzeug/routing.py in ), It contains a list , The list element is Rule Example , namely url To endpoint Mapping (werkzeug/routing.py in ).add_url_rule The second function of is to url_map Add Rule Example ( It is also in the application run It was done before )

Conclusion

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