Can you explain what is meant by stateful applications?

Applications with state preservation (stateful applications) are programs that save information about their current state between sessions or during operation. This allows the application to remember what happened previously and continue working without data loss.

For example, in a web application, a user's session can save data about selected items in the cart, so that this information is not lost when navigating between pages.

In Python, such behavior can be implemented by saving state in files, databases, or sessions. For example, serializing an object to a file:

import pickle

state = {'counter': 5, 'user': 'Alice'}

# Save state
with open('state.pkl', 'wb') as f:
    pickle.dump(state, f)

# Load state
with open('state.pkl', 'rb') as f:
    loaded_state = pickle.load(f)
print(loaded_state)