import-layers (BTARCH001)¶

Added in 0.12.0 · Stable · Enabled by default (error)

Family: architecture · Standard: CES-5 · Languages: python

Directive¶

The option layers lists the layers of the project from the top one down, each a Python module or several modules separated by |. A module of a layer imports nothing of a layer above it, and the modules separated by | in one layer import nothing of each other. botica lint reports each import statement that breaks this, at the statement, and also an import of a module in no layer that leads, through other modules in no layer, to a module that the importer may not import; the message shows that chain. The rule runs once for the whole project, on every botica lint. An error by default; without layers it reports nothing.

A module is in a layer when it is the module of the layer or a module inside it. The first part of the name of each module of the layers is a top package. The module of a file is its path from the folder that holds its top package: the root of the project, else src/, else the shallowest folder that holds it; the files of the package in other folders (tests/app/…) are left out. An import names the longest module of the project its name starts with (from app.api import router names app.api when router is no module), and a relative import starts from the package of its file. Every import counts, inside a function or an if TYPE_CHECKING: block too.

Why¶

When core cannot import api, the lower layers stay usable and testable without the upper ones, and the dependency graph stays acyclic. A rule makes the direction a failure of the run instead of something that a review has to notice.

Do¶

TOMLPython

[rules.import-layers]
layers = ["app.entrypoints", "app.api", "app.database | app.impl", "app.core"]

# app/api/routes.py
from app.core.models import Order

Don't¶

PythonPython

# app/core/models.py
from app.api.routes import router

# app/database/tables.py
from app.impl.service import price

Options¶

layers (strings, empty by default): the layers from the top one down, e.g. ["app.entrypoints", "app.api", "app.database | app.impl", "app.core"].

Suppression¶

The rule is of project scope, and only the configuration of botica silences it: the path in extend-ignores of [rules.import-layers], or ignore = ["import-layers"]. A comment that names it is invalid-suppression.