dict

A dictionary, often abbreviated as dict in programming, is a data structure that stores associations between keys and values. It provides fast lookup of a value by its key and supports insertion, update, and deletion of entries. Most implementations are based on a hash table, which yields efficient average-case performance for common operations.

In Python, dict is the built-in mutable mapping type that maps hashable keys to values. Similar structures appear in other languages, such as HashMap or Map in Java, std::unordered_map in C++, and Dictionary types in C#. These containers may or may not preserve insertion order, depending on the language and implementation.

Core operations include creating an empty dictionary, assigning or updating a value for a key, retrieving a value by key (often with a default for missing keys), and removing entries. Common views expose keys, values, and items for iteration, and there are convenience helpers for safe lookups and default values.

Key properties typically require that keys are hashable and immutable so their hash remains constant. Values may be of any type. A dictionary uses a hash function to determine position and handles collisions through techniques such as chaining or open addressing. Memory usage depends on capacity and density of entries.

Dicts are widely used to implement associative arrays, caches, configuration stores, and indexing structures. They offer average-case constant time complexity for lookups and updates, with performance degrading in worst-case scenarios. Variants include ordered, immutable, or specialized mappings such as default or sorted dictionaries.