Nested Loops

Concepts covered: pyNestedLoops

A nested loop is a loop inside another loop. The inner loop runs completely for each iteration of the outer loop. This pattern is essential for working with multi-dimensional data structures and generating combinations. Basic Nested Loop The inner loop completes all its iterations before the outer loop moves to the next item: The outer loop runs 3 times. For each outer iteration, the inner loop runs 2 times. Total iterations: 3 x 2 = 6. Working with 2D Data Nested loops are natural for processing matrices (lists of lists): Generating Combinations Nested loops naturally generate all combinations of elements: Triangle and Pyramid Nested loops where the inner loop depends on the outer loop create triangle patterns. This is common for comparisons and hierarchical displays: In the unique pairs

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This section is part of the Loops: Intermediate 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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