Flask: how to store and retrieve a value bound to the request

Question

I want to store a value that is bound to a Flask request, I want the value to live only as long at the request and it should be availablbe in @app.after_request, how would the get_my_request_var and set_my_request_var be implemented in the code below ?

@app.route("/aRoute")
def a_function():
    set_my_request_var('aName', request, 123)


@app.after_request
def per_request_callbacks(response):

    v = get_my_request_var('aName', request)

    return response

Answer 1

I'd set a value on the flask.g globals object and retrieve that in the after_request handler:

def set_my_request_var(name, value):
    if 'my_request_var' not in g:
        g.my_request_var = {}
    g.my_request_var[name] = value


@app.after_request
def per_request_callbacks(response):
    values = g.get('my_request_var', {})
    v = values.pop('aName')

    return response


@app.route("/aRoute")
def a_function():
    set_my_request_var('aName', 123)

The values.pop() removes the key from the my_request_var dictionary on the global flask.g context, so that a future request won't have to handle it.

The global flask.g context is thread safe and tied to the current request; quoting from the documentation:

The application context is created and destroyed as necessary. It never moves between threads and it will not be shared between requests.

Another option is to not handle this in a after_request handler. Use the newer @flask.after_this_request() decorator instead to register a callback for just this request:

from flask import after_this_request


@app.route("/aRoute")
def a_function():
    aName = 123

    @after_this_request
    def this_request_callback(response)
        # do something with `aName` here
        return response            

or, in a helper function:

def something_after_this_request(aName):
    @after_this_request
    def this_request_callback(response)
        # do something with `aName` here
        return response            


@app.route("/aRoute")
def a_function():
    something_after_this_request(123)