Execution Flow

Understanding how Python decides which lines to execute is fundamental to writing correct programs. In Python, indentation is not just for readability; it determines which code belongs together and when it runs. Indentation and Execution When you indent code under an if statement, you are telling Python: "only run these lines if the condition is True." The indentation level defines a block of code that executes together: The two indented print statements form a single block. They either both run (when is_raining is True) or both get skipped (when False). The unindented line runs regardless of the condition. When Python encounters an if-elif-else chain, it follows a predictable sequence of steps to determine which block to execute: Nested Blocks You can place if statements inside other if s

About This Interactive Section

This section is part of the Control Flow: 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.