The HTTP protocol is stateless, meaning that requests are independent from each other, and hence there is no sort of data persistance. There is a need to store and transmit data, and it can be achieved in several ways

Client Side Storage

Cookies

Cookies are data elements that are stored on the client.
Each time a request is made, all the cookies are sent to the server.

Cookies have a ‘lifetime’ - that is, they expire after a certain time.

Flask

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@app.route("/doSomething")
def something():
  return request.cookies["name"]

Secure Cookies in Flask

Because cookies are insecure (they can be easily tampered), Flask provides a mechanism to securely stored data - using Flask’s session feature

Note: The session is just an encrypted cookie with the name session

Setup
1) Import session
from Flask import session
2) Set up the secret key (the encryption key)
(app:Flask).secret_key = YOUR_SECRET_KEY

In your request context, you can then treat session as a dictionary.

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@app.route("/blah")
def someRouteFunction():
  return session["name"]

JavaScript - localStorage

The drawback to cookies, is that all the cookies are sent to the server.
i.e When writing a web app, there may be security and privacy concerns about transmitting confidential user data.

localStorage is bound to the domain name of the website, and exists for an infinite lifetime.

localStorage.get(key)
localStorage.set(key)
localStorage.clear()

JavaScript - sessionStorage

For non-persistent storage (ie data that gets destroyed when the page is closed), there exists sessionStorage

sessionStorage.get(key)
sessionStorage.set(key)
sessionStorage.clear()

Server Side Storage

We can also store session information on the server, which involves each client being mapped to a key in the server