How Computers Store Data

Before we can understand variables, we need to understand memory. Your computer has two main types of storage: When you run a Python program, it uses RAM to store all the data it needs. Think of RAM as a massive grid of tiny storage slots, each with a unique address (like a house number on a street). Each slot can hold a small piece of data. When you create a variable in Python, you're essentially telling the computer: "Reserve some of these memory slots for me, and let me refer to them by this name." Memory and variables are the foundation of every program you will ever write. Every piece of data your program works with lives in a named memory slot.

About This Interactive Section

This section is part of the Python Expressions: Beginner lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

How DataDriven Lessons Work

DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.