how do i create a dict of class objects, persist them on disk and access them later?

Basically i'm trying to design an Command-line ATM with User as my class. Later i want to load this objects from disk and perform following operations on it.

• signup
• authentication
• pay
• rewards
• balance check
• pin change
• last n statement print
• report a complaint

now my main concern is how this can be done dynamically, in-memory and store the final result in disk as pickle or something