Iterating with for Loops

Concepts covered: pyForBasic

A for loop repeats a block of code once for each item in a sequence. Without one, processing fifty files means writing fifty nearly-identical blocks of code. A loop collapses all of that into three lines. Basic for Loop Syntax Looping Over Strings Strings are sequences of characters, so you can loop over them character by character: Each character in the string becomes the loop variable in turn. This is useful for analyzing text character by character. Accumulating Results A common pattern is to build up a result as you loop through items. Initialize an accumulator before the loop, then update it inside: Building New Lists You can create new lists by looping through existing ones and appending transformed items: This pattern of initializing an empty list before the loop and appending items

About This Interactive Section

This section is part of the Loops: 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.

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