Calling and Storing

Defining a function creates it but does not execute it. The function body only runs when you explicitly call the function by writing its name followed by parentheses containing any required arguments. You can call a function as many times as needed, and each call is independent. The results can be used directly, stored in variables, or passed to other functions. Functions Calling Functions Functions can call other functions. This is how you build complex programs from simple, well-tested pieces. Each function handles one specific task, and higher-level functions combine them to accomplish larger goals. This approach is called functional decomposition, and it is fundamental to writing maintainable software. Real Data Pipeline Pattern Professional data engineers structure ETL pipelines as ch

About This Interactive Section

This section is part of the Functions: 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.