ordered-set
An OrderedSet is a custom MutableSet that remembers its order, so that every
Decision gist · record as of 2026-08-14
Yes, if you need ordered set semantics with index access and can tolerate dormant maintenance. The package is stable, has no dependencies, installs easily, and solves a real gap between sets and lists. Not recommended if you require active maintenance or expect frequent updates to track Python evolution.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Low friction installation as a pure-Python wheel with no runtime dependencies.
- Maintenance is dormant—last release was 2022-01-26 and no commits since 2024-08-09—but the package is marked Production/Stable and has been stable since its 2013 initial release.
License · maintenance · safety
permissive license (permissive) — Licensed under MIT (permissive), so you can use it freely in commercial and open-source projects without restriction or obligation to share modifications.
last release 2022-01-26 (1661 days) · last repo commit 2024-08-09 · 230 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 41,161,286 downloads/mo, #675 on PyPI
Alternatives
Verify before relying
pip install ordered-set
from ordered_set import OrderedSet
letters = OrderedSet('abracadabra')
print(letters.index('r')) # 2
print(letters[2]) # 'r'- Whether dormant maintenance status affects long-term compatibility with future Python versions beyond 3.10
- Performance characteristics for very large sets compared to built-in dict-based ordered collections in Python 3.7+
What it is and what it does
OrderedSet is a data structure that behaves like a Python set—supporting membership testing, union, intersection, and difference operations—while also preserving insertion order and providing list-like index-based access. You can look up an element's position, retrieve an element by index, and perform fancy indexing with multiple indices at once.
It trades O(1) deletion for O(1) index lookups by storing content in a standard list rather than a linked list. This makes it useful in data science workflows where you need bidirectional mapping between sparse vocabularies and dense index numbers, and in cases where you want set semantics but also need to know or access elements by position. It implements standard collection protocols including pickling and generic type annotations.
Use it for
- Build a vocabulary index for NLP or machine learning that maps words to dense integer IDs while preserving order
- Deduplicate a sequence while keeping insertion order and enabling fast index-based lookups
- Implement a cache or registry where you need both O(1) membership testing and positional access
- Replace pandas.Index for lightweight ordered unique collections without the pandas dependency
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you need ordered set semantics with index access and can tolerate dormant maintenance.
The package is stable, has no dependencies, installs easily, and solves a real gap between sets and lists. Not recommended if you require active maintenance or expect frequent updates to track Python evolution.
Install
ordered-set on PyPI
Before you install
Low friction installation as a pure-Python wheel with no runtime dependencies. Maintenance is dormant—last release was 2022-01-26 and no commits since 2024-08-09—but the package is marked Production/Stable and has been stable since its 2013 initial release.
License in practice
Licensed under MIT (permissive), so you can use it freely in commercial and open-source projects without restriction or obligation to share modifications.
Quickstart
pip install ordered-set
from ordered_set import OrderedSet
letters = OrderedSet('abracadabra')
print(letters.index('r')) # 2
print(letters[2]) # 'r'Verify before relying
- Whether dormant maintenance status affects long-term compatibility with future Python versions beyond 3.10
- Performance characteristics for very large sets compared to built-in dict-based ordered collections in Python 3.7+
Package facts
| License | permissive license permissive |
| Python support | Supports the current Python release >=3.7 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Dormant 1,661 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 41,161,286 / month, #675 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseProgramming Language :: PythonProgramming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: PyPy |
Evidence: ordered_set-4.1.0-py3-none-any.whl
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Similar packages
Provides multiple ordered set implementations (OrderedSet, StableSet, OrderlySet, SortedSet) that maintain insertion order while supporting set operations like union, intersection, and difference.
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Install it if you need a hashable list-like container or want to enforce immutability after initialization.
Provides an OrderedDict implementation for Python 2.4–2.6, preserving insertion order in a dictionary-like object with O(1) amortized insertion, deletion, and lookup performance.
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Provides four specialized collection types—bag (multiset), setlist (ordered set), bijection (one-to-one mapping), and IndexedDict (ordered dict with index access)—as pure Python implementations with no external dependencies.
orderedmultidict provides a dictionary that stores multiple values per key while preserving insertion order, with an API compatible with Python's built-in dict.
See also llist · multiset · slicerator · nocasedict