svcs 23.21.0

A Flexible Service Locator for Python.

svcs (pronounced services) is a dependency container for Python. It gives you a central place to register factories for types/interfaces and then imperatively acquire instances of those types with automatic cleanup and health checks.

It's suitable for implementing Inversion of Control using either dependency injection or service location while not requiring global state, decorators, or mangling of function signatures.

Benefits:

• Eliminates tons of repetitive boilerplate code,
• unifies acquisition and cleanups of services,
• provides full static type safety for them,
• simplifies testing through loose coupling,
• improves live introspection and monitoring with health checks.

The goal is to minimize the code for acquiring pluggable services to:

from svcs.your_framework import svcs_from

def view(request):
    db, api, cache = svcs_from(request).get(Database, WebAPIClient, Cache)

... or less!

To a type checker like Mypy, db has the type Database, api has the type WebAPIClient, and cache has the type Cache. db, api, and cache will be automatically cleaned up when the request ends -- it's context managers all the way down.

svcs comes with seamless integration for AIOHTTP, FastAPI, Flask, Pyramid, and Starlette.

While svcs also has first-class support for static typing, it is strictly optional and will always remain so. svcs also doesn't check your types at runtime. It only forwards the type you have asked for to the type checker. If you don't use a type checker, that information is ignored without any runtime overhead.

Read on in Why? if you're intrigued!

Project Links

• PyPI
• GitHub
• Documentation
• Changelog
• Funding

Release Information

Changed

• Backwards-Incompatible: Since multiple people have been bit by the enter=True default for Registry.register_value(), and it's very early in svcs life, we're changing the default to enter=False for all versions of register_value().

  This means that you have to explicitly opt-in to context manager behavior which makes a lot more sense for singletons like connection pools which are the most common candidates for registered values.

  (The irony of shipping a backwards-incompatible change in the release directly following the adoption of a backwards-compatibility policy not lost on me.) #50 #51

Added

• Container-local registries! Sometimes it's useful to bind a value or factory only to a container. For example, request metadata or authentication information.

  You can now achieve that with svcs.Container.register_local_factory() and svcs.Container.register_local_value(). Once something local is registered, a registry is transparently created and it takes precedence over the global one when a service is requested. The local registry is closed together with the container. #56

• Flask: svcs.flask.registry which is a werkzeug.local.LocalProxy for the currently active registry on flask.current_app.

Fixed

• We've stopped rewriting the public names of our objects and typing.get_type_hints() now works on them as expected for Python 3.10 and later. #52 #53

• The detection of container arguments in svcs.Registry() when using string-based type annotations is more robust now. #55

Full Changelog →

Credits

svcs is written by Hynek Schlawack and distributed under the terms of the MIT license.

The development is kindly supported by my employer Variomedia AG and all my fabulous GitHub Sponsors.

The Bestagon radar logo is made by Lynn Root, based on an Font Awesome icon. svcs has started out as a wrapper around wired by Michael Merickel and has been heavily influenced by it.