pyrsistent
Persistent/Functional/Immutable data structures
Decision gist · record as of 2026-08-14
Yes, if you need immutable collections and can tolerate aging maintenance. The library is stable, has no known vulnerabilities, installs with zero friction, and is widely used (top 1000 on PyPI). However, the last release was over 1000 days ago; verify that the package still meets your Python version and feature needs before committing to it for new projects.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Low install friction; pure Python wheel with no runtime dependencies.
- Maintenance is aging—last release was 1024 days ago—but the repository remains active and unarchived with solid community adoption (2196 stars).
License · maintenance · safety
MIT (permissive) — MIT license is permissive; you can use, modify, and distribute pyrsistent freely in commercial and open-source projects with minimal restrictions.
last release 2023-10-25 (1024 days) · last repo commit 2026-01-31 · 2,196 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 41,840,134 downloads/mo, #666 on PyPI
Alternatives
Verify before relying
pip install pyrsistent
from pyrsistent import v, m, s
# Immutable vector (like list)
v1 = v(1, 2, 3)
v2 = v1.append(4) # returns new vector, v1 unchanged
# Immutable map (like dict)
m1 = m(a=1, b=2)
m2 = m1.set('c', 3) # returns new map, m1 unchanged
# Immutable set
s1 = s(1, 2, 3)
s2 = s1.add(4) # returns new set, s1 unchanged- Performance characteristics (e.g., actual overhead vs. standard collections) under realistic workloads
- Compatibility with type checkers like mypy for persistent collection types
- Whether the aging maintenance status affects bug fixes or Python version support going forward
What it is and what it does
Pyrsistent is a library of immutable data structures designed to prevent hidden side effects in Python code. Instead of mutating collections in place, all write operations return a new copy with the requested changes, leaving the original untouched. This makes reasoning about program behavior simpler—you can trust that an object you hold a reference to will never be modified by code elsewhere in your application.
The library includes persistent versions of common Python collections: PVector (like list), PMap (like dict), PSet (like set), PRecord (a typed, fixed-field map), PClass (a typed Python class), PBag, PList, and PDeque. All are designed to share common elements through path copying for efficiency. The structures support standard Python protocols (Sequence, Mapping, Set, Hashable), making them drop-in replacements in many contexts, and can be converted to and from standard Python collections via freeze and thaw functions.
Use it for
- Building applications where immutability prevents accidental state mutations and simplifies debugging
- Using persistent collections as dictionary keys or set members (they are hashable)
- Implementing undo/redo systems by keeping historical versions of data structures
- Writing concurrent code where shared immutable data eliminates race conditions
- Defining data records with optional type checking and fixed fields (PRecord, PClass)
- Transforming nested persistent structures (maps and vectors) with the transform API
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you need immutable collections and can tolerate aging maintenance.
The library is stable, has no known vulnerabilities, installs with zero friction, and is widely used (top 1000 on PyPI). However, the last release was over 1000 days ago; verify that the package still meets your Python version and feature needs before committing to it for new projects.
Install
pyrsistent on PyPI
Before you install
Low install friction; pure Python wheel with no runtime dependencies. Maintenance is aging—last release was 1024 days ago—but the repository remains active and unarchived with solid community adoption (2196 stars).
License in practice
MIT license is permissive; you can use, modify, and distribute pyrsistent freely in commercial and open-source projects with minimal restrictions.
Quickstart
pip install pyrsistent
from pyrsistent import v, m, s
# Immutable vector (like list)
v1 = v(1, 2, 3)
v2 = v1.append(4) # returns new vector, v1 unchanged
# Immutable map (like dict)
m1 = m(a=1, b=2)
m2 = m1.set('c', 3) # returns new map, m1 unchanged
# Immutable set
s1 = s(1, 2, 3)
s2 = s1.add(4) # returns new set, s1 unchangedVerify before relying
- Performance characteristics (e.g., actual overhead vs. standard collections) under realistic workloads
- Compatibility with type checkers like mypy for persistent collection types
- Whether the aging maintenance status affects bug fixes or Python version support going forward
Package facts
| License | MIT permissive |
| Python support | Supports the current Python release >=3.8 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Aging 1,024 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 41,840,134 / month, #666 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Intended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseOperating System :: OS IndependentProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Programming Language :: Python :: Implementation :: PyPy |
Evidence: pyrsistent-0.20.0-py3-none-any.whl
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