References and Shallow Copies

Concepts covered: pyListCopy

Before understanding deep copies, you must understand how Python handles object references. When you assign a list to a variable, the variable does not contain the list itself. Instead, it contains a reference (essentially a pointer) to where the list lives in memory. This distinction is crucial. Reference semantics affect every operation you perform on lists. Here are the key rules that govern how Python variables interact with list objects. Variables Are References The Aliasing Problem Since both variables point to the same object, modifying through one variable affects the other. This is called aliasing, and it can cause unexpected behavior if you are not aware of it. We only modified alias, but original shows the same changes. This is not a bug; it is the expected behavior when two var

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This section is part of the Lists: Advanced 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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