---
id: pyrsistent
version: "0.20.0"
license: MIT
license_treatment: permissive
maintenance: aging
---

# pyrsistent — Persistent/Functional/Immutable data structures

License: permissive · Maintenance: aging · Popularity: top 1,000 on PyPI

## Install

pip install pyrsistent
uv add pyrsistent
poetry add pyrsistent

## Description

Pyrsistent
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.. image:: https://github.com/tobgu/pyrsistent/actions/workflows/tests.yaml/badge.svg
    :target: https://github.com/tobgu/pyrsistent/actions/workflows/tests.yaml


.. _Pyrthon: https://www.github.com/tobgu/pyrthon
.. _Pyrsistent_extras: https://github.com/mingmingrr/pyrsistent-extras

Pyrsistent is a number of persistent collections (by some referred to as functional data structures). Persistent in
the sense that they are immutable.

All methods on a data structure that would normally mutate it instead return a new copy of the structure containing the
requested updates. The original structure is left untouched.

This will simplify the reasoning about what a program does since no hidden side effects ever can take place to these
data structures. You can rest assured that the object you hold a reference to will remain the same throughout its
lifetime and need not worry that somewhere five stack levels below you in the darkest corner of your application
someone has decided to remove that element that you expected to be there.

Pyrsistent is influenced by persistent data structures such as those found in the standard library of Clojure. The
data structures...

## AI interpretation — verify before relying

Pyrsistent provides immutable, persistent collections (vectors, maps, sets, records, and more) where all mutations return new copies, leaving originals unchanged and eliminating hidden side effects.

Verdict: Pyrsistent is a mature, well-established library for functional-style immutable collections with zero runtime dependencies and permissive licensing. While aging (1000+ days since last release), its stable maintenance status, broad Python version support (3.8–3.12, PyPy), and absence of known vulnerabilities make it a reliable choice for projects requiring persistent data structures.

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