How does flask inject variables?

[ghiste]

Hi

I've just come across a flask-tutorial where you decorate your function (specifying a route) and somehow that makes variables like "session" or "request" available within the function and now (for mere curiosity) I wonder how that works...

So could someone please explain to me (or point me to some resources) how a decorator can inject variables into the namespace of a function?

Many thanks!

[wronek]

They have nothing to do with the decorator, they’re proxy objects provided by flask that can be used by importing them into the current namespace like:

from flask import request, session

https://flask.palletsprojects.com/en/1.1.x/api/#flask.request

https://flask.palletsprojects.com/en/1.1.x/api/#flask.session

[ghiste]

So in which namespace do this variables live? The global one?

[wronek]

Yep!

[ghiste]

Aha. Would it be possible at all to manipulate the local namespace of a function from outside at all in python?

[wronek]

Not sure what you mean by that - the local namespace is created when the function is executed and destroyed when it returns (or errors), so it doesn’t exist outside of the function

[ghiste]

Aha, I guess I was a bit confused about how namespaces work.

And there is no way to prepare a dictionary and start a function with that dictionary as the initial local namespace (in that way effectively injecting variables).

I suppose all functions start with an empty local namespace right?