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This article will explain in detail how Flask implements the request hook. Xiaobian thinks it is quite practical, so share it with you for reference. I hope you can gain something after reading this article.

In Web applications, sometimes some processing needs to be done before or after responding to requests. To avoid writing duplicate code for each view function, Flask provides request hooks that can be used to register processing functions that execute at different stages of request processing, so that we can easily perform pre-and post-processing on requests.

Flask common request hooks are as follows:

before_first_request: Run before the first request is processed

before_request: runs before each request and after each request if no unhandled exceptions are thrown

after_request: runs after each request if there are no unhandled exceptions thrown

teardown_request: runs at the end of each request, even if there are unhandled exceptions thrown

These request hooks are implemented using decorators, and the usage is very simple. They are basically the same as app.route() decorators. Here are some functions decorated with these request hooks to do some processing before and after each request, just printing a sentence for ease of understanding.

@app.before_first_requestdef before_first_request(): print('before_first_request')@app.before_requestdef before_request(): print('before_request')@app.after_requestdef after_request(response): print('after_request') return response@app.teardown_requestdef teardown_request(e): print('teardown_request')@app.route('/test')def test(): return 'test'

First request console output:

Second request console output:

Here are some common use cases for request hooks:

before_first_request: Run before the first request, can do some initialization of the Web program

before_request: Run before each request, and can perform database connection creation operations, user permission verification operations, etc.

After_request: We often perform database operations in view functions, such as updates, inserts, and then need to commit changes to the database. The code that commits changes can be placed in the function registered by the after_request hook.

teardown_request: Can receive exceptions from view functions, generally used to record error logs

Note: Each request hook can register any number of handler functions, and the function name does not have to be the same as the hook name. If there are multiple before_requests, the execution order is from top to bottom;after_request receives a response object and returns the same or updated response object, multiple after_requests are executed from bottom to top.

About "Flask how to implement the request hook" this article is shared here, I hope the above content can be of some help to everyone, so that you can learn more knowledge, if you think the article is good, please share it for more people to see.

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