Core-Lib

Core-Lib keeps Flask, SQLAlchemy, and external services out of your business logic — so changing them doesn't mean rewriting your app.

Without this separation, those dependencies spread through your codebase — and every future change gets more expensive.

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Most Python backends start simple — then slowly become tightly coupled:

• Your services import Flask's request
• Your business logic depends on SQLAlchemy sessions
• Your tests require real external services to run

Everything works — until you try to change something. Then it turns into a rewrite.

Core-Lib exists to prevent that.

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What it is

Core-Lib is an application-structure framework for Python backends — the place where your application lives, while everything else (web frameworks, databases, APIs) plugs into it from the outside.

Core-Lib doesn't invent a new pattern — it enforces one consistently, so it survives beyond the first few months of development — when shortcuts start creeping in.

class YourCoreLib(CoreLib):
    def __init__(self, config: DictConfig):
        CoreLib.__init__(self)
        db = SqlAlchemyConnectionFactory(config.core_lib.data.db)  # connection at the edge
        self.user = UserService(      # business logic
            UserDataAccess(db)        # database queries
        )

When the framework beneath you changes — and it will — you replace the thin web layer (not the entire codebase). Your services, data access, and most tests stay the same.

# Flask today
@app.route('/api/user')
def get_user():
    return response_json(app_instance.user.get(request.user.id))

# FastAPI tomorrow — UserService didn't change, not one line
@router.get('/api/user')
def get_user():
    return app_instance.user.get(current_user.id)

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What it is not

Not a web framework. No router, no request lifecycle. It works alongside Flask, Django, FastAPI — you bring the web layer.

Not a replacement for SQLAlchemy, Redis, or MongoDB. You still write SQLAlchemy models. You still use Redis commands. Core-Lib handles the connection lifecycle and stops those dependencies from spreading through your business logic.

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When to use it

Use it when:

• Your backend will live for years, not weeks
• Multiple engineers will touch the same codebase
• You want to run the same logic from web, jobs, scripts, and tests
• You need to swap infrastructure (DB, cache, HTTP client) without touching business logic

Don't use it when:

• Your app is a prototype, script, or simple CRUD app
• Your app is small and unlikely to change much

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Quickstart

pip install core-lib

Requirements: Python >= 3.7

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Documentation

Full documentation, examples, and guides: https://shay-te.github.io/core-lib/

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Running tests

python -m unittest discover -v

License

Core-Lib is licensed under MIT