Nested Dictionaries — Data Within Data

"A single expense isn't just an amount — it has a description, a category, a date, a payment method, and maybe notes. A real transaction record is a collection of related information. Nested dictionaries — dictionaries inside dictionaries — are how you model this kind of structured, complex data. Almost every real API response, database record, and configuration file uses nested dictionaries. Mastering them unlocks real-world data handling."