sortdicts

Sortdicts are dictionary-like data structures designed to keep their keys in sorted order. They map keys to values while presenting iteration and access in a defined key order. Depending on the implementation, sorting may be maintained automatically as items are inserted or deferred until traversal. They are commonly used when ordered iteration or range queries over keys are important.

In practice, sortdicts appear in several programming ecosystems. In Python, there is no built-in sortdict, but libraries such as sortedcontainers provide a SortedDict implementation that keeps keys sorted as items are inserted. Earlier, Django included a SortedDict class (in django.utils.datastructures) that emulated a sorted mapping, but it was deprecated and removed in recent releases. In Java, a similar concept is provided by TreeMap, which implements a map ordered by its keys via a balanced tree. In C++, std::map offers an ordered map keyed by the sort criterion. Many other languages provide analogous ordered-map data structures.

Complexity and behavior typically reflect the underlying data structure. Most sortdict implementations rely on balanced search trees, giving O(log n) time for insertion, deletion, and lookup, and ordered iteration over keys. Some variants allow custom comparators to define the sort order. Memory usage is usually higher than hash-based maps due to pointers and tree structure.

Common use cases include producing reports or logs where output must be in key order, performing range-based queries (keys within a given interval), or maintaining a persistent index that must be traversed in ascending order.

Limitations and considerations include availability in standard libraries, performance depending on the underlying structure, and the need for comparable keys or a comparator. They are often not thread-safe by default and may introduce greater overhead than unordered maps. See also: TreeMap, std::map, SortedContainers, OrderedDict.