Defining Functions

Functions are reusable blocks of code that perform a specific task. They help you organize your programs and avoid repeating the same code. What is a Function? Why Create Functions? Built-in functions cover common operations, but your programs have unique requirements. You might need to calculate taxes for your specific business rules, format names according to your company standards, or validate data in ways Python cannot predict. Creating your own functions lets you package this custom logic and reuse it throughout your program. Consider a program that needs to calculate the area of rectangles in several places. Without functions, you would repeat the calculation each time: The calculation width * height appears three times. This seems harmless now, but imagine the formula becomes more c

About This Interactive Section

This section is part of the Functional Programming: 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.