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Sorted Containers -- Sorted List, Sorted Dict, Sorted Set

Project description

Sorted Containers is an Apache2 licensed sorted collections library, written in pure-Python, and fast as C-extensions.

Python’s standard library is great until you need a sorted collections type. Many will attest that you can get really far without one, but the moment you really need a sorted list, sorted dict, or sorted set, you’re faced with a dozen different implementations, most using C-extensions without great documentation and benchmarking.

In Python, we can do better. And we can do it in pure-Python!

>>> from sortedcontainers import SortedList
>>> sl = SortedList(['e', 'a', 'c', 'd', 'b'])
>>> sl
SortedList(['a', 'b', 'c', 'd', 'e'])
>>> sl *= 10_000_000
>>> sl.count('c')
>>> sl[-3:]
['e', 'e', 'e']
>>> from sortedcontainers import SortedDict
>>> sd = SortedDict({'c': 3, 'a': 1, 'b': 2})
>>> sd
SortedDict({'a': 1, 'b': 2, 'c': 3})
>>> sd.popitem(index=-1)
('c', 3)
>>> from sortedcontainers import SortedSet
>>> ss = SortedSet('abracadabra')
>>> ss
SortedSet(['a', 'b', 'c', 'd', 'r'])
>>> ss.bisect_left('c')

All of the operations shown above run in faster than linear time. The above demo also takes nearly a gigabyte of memory to run. When the sorted list is multiplied by ten million, it stores ten million references to each of “a” through “e”. Each reference requires eight bytes in the sorted container. That’s pretty hard to beat as it’s the cost of a pointer to each object. It’s also 66% less overhead than a typical binary tree implementation (e.g. Red-Black Tree, AVL-Tree, AA-Tree, Splay-Tree, Treap, etc.) for which every node must also store two pointers to children nodes.

Sorted Containers takes all of the work out of Python sorted collections - making your deployment and use of Python easy. There’s no need to install a C compiler or pre-build and distribute custom extensions. Performance is a feature and testing has 100% coverage with unit tests and hours of stress.


Alex Martelli, Fellow of the Python Software Foundation

“Good stuff! … I like the simple, effective implementation idea of splitting the sorted containers into smaller “fragments” to avoid the O(N) insertion costs.”

Jeff Knupp, author of Writing Idiomatic Python and Python Trainer

“That last part, “fast as C-extensions,” was difficult to believe. I would need some sort of Performance Comparison to be convinced this is true. The author includes this in the docs. It is.”

Kevin Samuel, Python and Django Trainer

I’m quite amazed, not just by the code quality (it’s incredibly readable and has more comment than code, wow), but the actual amount of work you put at stuff that is not code: documentation, benchmarking, implementation explanations. Even the git log is clean and the unit tests run out of the box on Python 2 and 3.

Mark Summerfield, a short plea for Python Sorted Collections

Python’s “batteries included” standard library seems to have a battery missing. And the argument that “we never had it before” has worn thin. It is time that Python offered a full range of collection classes out of the box, including sorted ones.

Sorted Containers is used in popular open source projects such as: Zipline, an algorithmic trading library from Quantopian; Angr, a binary analysis platform from UC Santa Barbara; Trio, an async I/O library; and Dask Distributed, a distributed computation library supported by Continuum Analytics.


  • Pure-Python
  • Fully documented
  • Benchmark comparison (alternatives, runtimes, load-factors)
  • 100% test coverage
  • Hours of stress testing
  • Performance matters (often faster than C implementations)
  • Compatible API (nearly identical to older blist and bintrees modules)
  • Feature-rich (e.g. get the five largest keys in a sorted dict: d.keys()[-5:])
  • Pragmatic design (e.g. SortedSet is a Python set with a SortedList index)
  • Developed on Python 3.7
  • Tested on CPython 2.7, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7 and PyPy, PyPy3


Installing Sorted Containers is simple with pip:

$ pip install sortedcontainers

You can access documentation in the interpreter with Python’s built-in help function. The help works on modules, classes and methods in Sorted Containers.

>>> import sortedcontainers
>>> help(sortedcontainers)
>>> from sortedcontainers import SortedDict
>>> help(SortedDict)
>>> help(SortedDict.popitem)


Complete documentation including performance comparisons is available at

User Guide

For those wanting more details, this part of the documentation describes introduction, implementation, performance, and development.

API Documentation

If you are looking for information on a specific function, class or method, this part of the documentation is for you.

Sorted Containers License

Copyright 2014-2018 Grant Jenks

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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