Basic introduction to flask 6 - Context

Flask Context ：

 

Actually in Flask There are two contexts in the project ： One is the application context （app）, The other is the request context （request）.

 

Request context request And application context current_app Is a global variable . All requests are shared .Flask There is a special mechanism to ensure that the data requested each time is isolated , namely A The data generated by the request will not affect B request . So you can import request object , Will not be affected by some dirty data , And you don't need to use request When it comes to request object . There is no need to understand in detail the specific implementation methods and principles of these two contexts . Just understand the four attributes of these two contexts ：

(1)request： Object on request context . This object is generally used to store some requested variables . such as method、args、form etc. .

(2)session： Object on request context . This object is generally used to store some session information .

(3)current_app： Returns the current app.

(4)g： Objects on the application context . Objects used as temporary storage when processing requests .

 

Common hook function

1. before_first_request： Execute before processing the first request . For example, the following code ：

 

@app.before_first_requestdef first_request():

    print 'first time request'

2.before_request： Execute before each request . You can usually use this decorator to add some variables to the view function . For example, the following code ：

@app.before_requestdef before_request():

    if not hasattr(g,'user'):

      setattr(g,'user','xxxx')

3.teardown_appcontext： No matter whether there is any abnormality , Registered functions are executed after each request .

@app.teardown_appcontext

def teardown(exc=None):

if exc is None:

db.session.commit()

else:

db.session.rollback()

db.session.remove()

·

4.template_filter： In the use of Jinja2 Customize filters when creating templates . For example, you can add one upper Filter （ Of course Jinja2 This filter already exists ）：

@app.template_filter

def upper_filter(s):

    return s.upper()

5.context_processor： Context processor . The keys in the returned dictionary can be used in the context of the template . for example ：

@app.context_processor

def my_context_processor():

    return {'current_user':'Anthony'}

6.errorhandler：errorhandler Receiving status code , You can customize the processing method of the response that returns this status code . for example ：

@app.errorhandler(404)

def page_not_found(error):

    return 'This page does not exist',404