lagom

What it is and what it does

Lagom is a dependency injection container that uses Python type hints to automatically construct and wire dependencies with minimal configuration. Most of your application code remains unaware of the container; Lagom is invoked only at the top level to assemble the dependency graph. It supports type-based auto-wiring where the container inspects `__init__` method type annotations and recursively builds instances, explicit singleton registration, lambda-based factory functions, and decorators for integrating with web frameworks and async code.

The design philosophy emphasizes minimal intrusion into existing code—you don't need to modify your classes to use Lagom, only to add type hints if you want auto-wiring. It's thread-safe at runtime and fully integrated with mypy for static type checking, making it suitable for both small scripts and larger applications that need structured dependency management without heavyweight framework overhead.

Use it for:

• Auto-wire dependencies in a web application by registering handler functions with the container and letting it inject services based on type hints.
• Manage expensive-to-create singleton instances (database connections, caches) by registering them once and reusing across the application.
• Gradually introduce dependency injection into an existing codebase by adding type hints to constructors without refactoring the rest of the code.
• Build testable code by swapping real dependencies with mocks in test containers without modifying production classes.
• Structure async Python applications where coroutines need injected dependencies resolved at startup.

Worth the install?

AI-flagged interpretation of the facts on this page — verify before relying

Lagom is a lightweight dependency injection container that auto-wires dependencies based on type hints, requiring zero configuration for most use cases.

Yes. Lagom is a solid choice for projects needing lightweight dependency injection without framework overhead. Zero runtime dependencies, active maintenance, broad Python version support, and a permissive MIT license make it low-risk. The type-hint-based design integrates well with modern Python tooling. Best suited for teams comfortable with type annotations and seeking minimal configuration; not necessary for very small scripts but valuable for any structured application.

Install

lagom on PyPI

pip install lagom

uv add lagom

poetry add lagom

Installing lagom

Before you install

Low install friction with no runtime dependencies. Actively maintained with a recent release (394 days ago) and ongoing commits; supports Python 3.7 through 3.13.

License in practice

MIT license permits unrestricted use, modification, and distribution in both open-source and commercial projects with minimal obligations.

Quickstart

pip install lagom

from lagom import Container

class MyDataSource:
    pass

class SomeClass:
    def __init__(self, datasource: MyDataSource):
        self.datasource = datasource

container = Container()
instance = container[SomeClass]

Verify before relying

• Performance characteristics and overhead compared to manual dependency management or other DI frameworks.
• Scope of framework integrations beyond the mentioned web framework hooks.
• Thread-safety guarantees under concurrent container access patterns.

Package facts

Evidence: lagom-2.7.7-py3-none-any.whl

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