Import-linter was useful for layered architecture in Python

Overview

Even when developing in Python, the design may be based on a layered architecture. At that time, you may want to check the direction of dependence.

project_root/
  ├ infrastructure/
  │ └ db
  ├ interface/
  │ └ controllers
  ├ application/
  │ └ service
  └ domain/
    └ entity

As an example, consider the above package configuration. Suppose you define the direction of the dependency in the form infrastructure-> interface-> application-> domain. You can easily fix it by using import-linter to automatically check for imports that break the rules during development.

Sample repository is available. See here for the entire source code.

How to use

$ pip install import-linter

Define the layer definition and dependency direction with setup.cfg or .importlinter. First, define the layer in the [importlinter] section.

[importlinter]
root_packages =
    infrastructure
    interface
    application
    domain

type = layers is a rule setting for layered architecture. The direction of dependence is expressed in the order of layers.

[importlinter:contract:1]
name = layered architecture contract
type = layers
layers =
    infrastructure
    interface
    application
    domain

There are various options (https://github.com/seddonym/import-linter/tree/master/docs) that allow you to configure flexible rules. For example, if you want to limit the import of flask packages to a specific layer, you can enable include_external_packages and define it with type = forbidden as shown below.

[importlinter]
root_packages =
    infrastructure
    interface
    application
    domain
include_external_packages = True

[importlinter:contract:2]
name = Do not use `flask` outside the interface layer.
type = forbidden
source_modules =
    infrastructure
    application
    domain
forbidden_modules =
    flask

To check

After completing the rule settings, check with the following command.

$ lint-imports

pipenv run lintfix                                                                                                                            ✘ 1 main ✚ ✱ ◼
Skipped 2 files
=============
Import Linter
=============

---------
Contracts
---------

Analyzed 14 files, 15 dependencies.
-----------------------------------

Layered architecture contract BROKEN
Do not use `flask` outside the interface layer. BROKEN

Contracts: 0 kept, 2 broken.


----------------
Broken contracts
----------------

Layered architecture contract
-----------------------------

domain is not allowed to import application:

- domain.entity -> application.repository (l.5)


Do not use `flask` outside the interface layer.
-----------------------------------------------

infrastructure is not allowed to import flask:

-   infrastructure.db -> domain.entity (l.4)
    domain.entity -> flask (l.3)


application is not allowed to import flask:

-   application.repository -> domain.entity (l.4)
    domain.entity -> flask (l.3)

-   application.service -> domain.entity (l.6)
    domain.entity -> flask (l.3)


domain is not allowed to import flask:

-   domain.entity -> flask (l.3)

If there is code that violates the rule, it will display an error.

Let's define it in the CI tool and have it checked at the time of PR.