---
id: eventsourcing
version: "9.5.4"
license: unclear
license_treatment: permissive
maintenance: active
---

# eventsourcing — Event sourcing in Python

License: permissive · Maintenance: active · Downloads: 91.5K/mo

## What it is and what it does

Eventsourcing provides a framework for building applications where every state change is recorded as an immutable event. Rather than storing current state directly, you define domain aggregates (like a Dog class) decorated with @event methods, then use an Application class to manage persistence and retrieval. The library handles event storage, replay, snapshotting, versioning, and optional encryption—supporting multiple backends (in-memory, SQLite, and external databases) configured through environment variables.

The core workflow is: define domain models with event decorators, create an application class that orchestrates saves and queries, then run your code against any configured persistence layer. Built-in features include optimistic concurrency control, compression, application-level encryption for PII compliance, and notification-based projections for CQRS patterns. It requires Python 3.10+ and depends only on typing_extensions.

Use it for:

- Build audit-trail systems where every state change must be recorded and replayed for compliance or debugging
- Implement CQRS architectures with separate read and write models using notifications and projections
- Create domain-driven applications with strong consistency boundaries and event-based communication between aggregates
- Develop distributed systems where event logs serve as the source of truth for replication across nodes
- Encrypt sensitive domain events at the application level to meet GDPR or similar data protection requirements

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Eventsourcing is a Python library for implementing event sourcing, a design pattern where all application state changes are stored as a sequence of immutable events that can be replayed to reconstruct state.

Yes. Eventsourcing is a mature, actively maintained library (stable since 2015, production-ready) with low install friction, no security vulnerabilities, and a permissive license. It's the right choice if you need event sourcing as a core pattern; if you're unsure whether event sourcing fits your problem, evaluate that architectural decision first before installing.

## Install

pip install eventsourcing
uv add eventsourcing
poetry add eventsourcing

## Installing eventsourcing

Before you install: Low friction: pure Python wheel with a single runtime dependency (typing_extensions). Actively maintained with a recent release 140 days ago and ongoing commits; repository shows 1681 stars and is not archived.

License in practice: Permissive license allows commercial and private use without restriction; suitable for most projects without legal concern.

Quickstart:

pip install eventsourcing

from eventsourcing.domain import Aggregate, event
from eventsourcing.application import Application

class Dog(Aggregate):
    @event('Registered')
    def __init__(self, name: str) -> None:
        self.name = name

class DogSchool(Application):
    def register_dog(self, name: str):
        dog = Dog(name)
        self.save(dog)
        return dog.id

school = DogSchool()
dog_id = school.register_dog('Fido')

Requires Python 3.10 or later; by default events are stored in memory using Python objects, but persistence modules can be configured via environment variables.

Verify before relying:

- Performance characteristics under high-volume event streams or with large aggregates
- Scalability limits when using in-memory persistence versus external databases
- Compatibility of encryption/compression features with all supported database adapters

## Package facts

- License: not declared (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 91.5K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

event sourcing library, event store python, domain-driven design ddd, cqrs event sourcing, event replay state management, aggregate event sourcing, domain events python, event-sourcing, domain-driven-design, cqrs

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