Layer Enforcer

Layer Enforcer is a tool for linting your imports within the project.

The tool was designed to help maintain following order of things:

• Dependencies always flow towards root of the tree. Often this is domain layer.
• Dependencies may skip layers, as long as they flow in same direction. For instance, your web layer may import use cases from domain layer.
• Infer layer from imports or module names. Say, if you import fastapi anywhere on the chain, the module is assigned to web layer, or maybe you want models to always be db layer.
• Flexible layer structure. Preferably defined via config file.
• Code is packaged by component. I.e. single component may contain code from the different layers.

Be warned, since this might not the best fit for you.

Algorithm

First pass: Match modules to layers. Report conflict if single module match more than one layer.

Second pass: For each module, iterate through all the imported modules. If current module has no assigned layer, assign first found layer within list of imported modules. If current module has an assigned layer, report conflict if import is not allowed.

Installation

pip install layer-enforcer

For Development

pip install -e .[test,lint]

Usage

layer-enforcer myproject myotherproject --layers layers.yml

pyproject.toml

Instead of explicitly specifying CLI arguments, it is possible to provide configuration via pyproject.toml within the tool.layer_enforcer table:

[tool.layer_enforcer]
modules = ["myproject", "myotherproject"]
ignore = ["myproject.containers"]
layers = "layers.yml"

layers.yml

An example of clean-architecture-ish layer layout for typical web app:

name: domain
submodules: ["entities", "use_cases"]
layers:
- name: service
  submodules: ["services"]
  layers:
  - name: infrastructure
    imports: ["stripe", "requests", "passlib"]
    layers:
    - name: db
      imports: ["sqlalchemy", "psycopg2", "alembic"]
      submodules: ["models", "memory", "database"]
    - name: web
      imports: ["fastapi", "jose"]
      submodules: ["views", "schemas"]
    - name: tasks
      imports: ["celery"]
      submodules: ["tasks"]