---
id: venusian
version: "3.1.1"
license: BSD-derived (Repoze)
license_treatment: permissive
maintenance: dormant
---

# venusian — A library for deferring decorator actions

License: permissive · Maintenance: dormant · Downloads: 2.9M/mo

## What it is and what it does

Venusian is a decorator deferral library used primarily by web frameworks and Zope-based systems. Instead of executing decorator logic when a function or class is decorated at import time, venusian lets you attach metadata to the decorated object and then run all registered callbacks during a separate "scan" phase. This separation is useful when you need to defer decisions until after all modules are loaded, or when you want to collect and process decorations in batch.

The library works by attaching callbacks to decorated objects via a `__venusian_callbacks__` attribute, then providing a Scanner that walks through packages and modules to invoke those callbacks. It handles edge cases like inherited decorations, imported objects that shouldn't be double-scanned, and metaclasses that don't behave normally. Venusian has no runtime dependencies and supports Python 3.7 through 3.13 on both CPython and PyPy.

Use it for:

- Building web frameworks that need to collect route or view decorations from multiple modules before setting up routing tables.
- Implementing plugin systems where decorators mark plugin entry points but registration must happen after all modules load.
- Creating configuration systems that defer decorator-driven setup until after dependency injection or configuration is complete.
- Zope-based applications that use decorators to register adapters, utilities, or event handlers in a deferred manner.
- Testing frameworks that need to collect test markers or fixtures from decorated functions without executing them at import time.

## Worth the install?

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

Venusian defers decorator actions from import time to a separate scan phase, allowing framework authors to register decorated functions and classes after modules are loaded rather than at decoration time.

Yes, if you are building a framework or plugin system that benefits from deferred decorator registration. Venusian is mature, well-tested, and has no dependencies. However, it is dormant (620 days since last release), so adopt it only if you are comfortable with minimal ongoing maintenance and can handle any issues yourself. For typical application code, you likely don't need it.

## Install

pip install venusian
uv add venusian
poetry add venusian

## Installing venusian

Before you install: Low friction: pure Python wheel with no runtime dependencies. Dormant maintenance (620 days since last release), but marked Mature and actively supports current Python versions through 3.13.

License in practice: BSD-derived Repoze license is permissive; you can use venusian in commercial and proprietary projects with minimal restrictions.

Quickstart:

pip install venusian

from venusian import Scanner

scanner = Scanner()
scanner.scan()

Verify before relying:

- Whether the scan phase can handle circular imports or complex module dependency graphs.
- Performance characteristics when scanning large codebases with many decorated objects.
- Specific use cases and integration patterns beyond the Pylons/Zope ecosystem.

## Package facts

- License: BSD-derived (Repoze) (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: dormant
- Downloads: 2.9M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

deferred decorator registration, decorator action deferral, scan-time decorator execution, framework decorator pattern, delayed decorator activation, decorator callback registration, import-time decorator deferral, decorator-pattern, framework-utility, zope-ecosystem

[View on SkillFed](https://skillfed.io/packages/venusian) · [View on PyPI](https://pypi.org/project/venusian/)