Unable to share variables between 2 flasks requests in a view function

Question

What I want is to share a variable between 2 flask requests! The variable is a large pandas dataframe.

I have read in this answer that i need to use g from flask global ! basically, I have 2 views function like this :

from flask import g
@home.route('/save', methods=['GET'])
def save_ressource():
    an_object = {'key': 'value'}
    setattr(g, 'an_object', an_object)
    return 'sucees'
@home.route('/read', methods=['GET'])
def read_ressource():
    an_object = getattr(g, 'an_object', None)
    if an_object:
        return 'sucess'
    else:
        return 'failure'

but this always return failure ie : None

and when i read in the documentation here it's said that :

Starting with Flask 0.10 this is stored on the application context and no longer on the request context which means it becomes available if only the application context is bound and not yet a request.

My question is how to solve this problem?

As said in the docs how can I bound application context?

Should I use sessions instead?

Any helps will be appreciate

the application should only work in localhost ! – Espoir Murhabazi Jan 26 '18 at 09:21 — Espoir Murhabazi, Jan 26 '18 at 09:21

score 8 · Accepted Answer · edited Jan 15 '20 at 23:12

8

The linked answer appears to be completely wrong. The g object is for storing global data from one function to another within the same request, and is not at all for sharing data between requests.

For that you need sessions:

from flask import Flask, session

@home.route('/save', methods=['GET'])
def save_ressource():
    an_object = {'key': 'value'}
    session['an_object'] = an_object
    return 'sucees'

@home.route('/read', methods=['GET'])
def read_ressource():
    an_object = session.get('an_object')
    if an_object:
        return 'sucess'
    else:
        return 'failure'

edited Jan 15 '20 at 23:12

ti7

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answered Jan 26 '18 at 09:11

Daniel Roseman

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okay, Thanks for the quick answer sir, But can this works if I want to save a large object?? ex a Dataframe?? – Espoir Murhabazi Jan 26 '18 at 09:19
2

Why wouldn't it? – Daniel Roseman Jan 26 '18 at 09:23
2

the reason is that a dataframe is not JSON serializable. – Espoir Murhabazi Jan 26 '18 at 09:42
But you can create a [custom encoder](http://flask.pocoo.org/snippets/119/) to handle any object and serialize it. – Renan Gomes Jan 23 '19 at 17:33
2

@EspoirMurhabazi you can use `df.to_dict()` and `df.to_json()` methods to serialize your dataframe to use across sessions. – spitfiredd Mar 14 '19 at 11:23

Unable to share variables between 2 flasks requests in a view function

1 Answers1

Linked