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https://github.com/jwbargsten/pytest-archon

Rule your architecture like a real developer
https://github.com/jwbargsten/pytest-archon

architecture archunit python

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Rule your architecture like a real developer

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# pytest-archon



[![build_and_test](https://github.com/jwbargsten/pytest-archon/actions/workflows/tests.yml/badge.svg)](https://github.com/jwbargsten/pytest-archon/actions/workflows/tests.yml)



`pytest-archon` is a little tool that helps you structure (large) Python projects. This

tool allows you to define architectural boundaries in your code, also known as

_forbidden dependencies_.



Explicitly defined architectural boundaries helps you keep your code in shape. It avoids

the creation of circular dependencies. New people on the project are made aware of the

structure through a simple set of rules, instead of lore.



## Installation



The simple way:



```sh

pip install pytest-archon

```



## Usage



_pytest-archon_ can be used to define architectural boundaries from (unit) tests.

Because they're tests, they can be closely tied to the actual application.



You can use _pytest-archon_ in tests by simply importing the `archrule` function. Using

this function you can construct import tests:



```python

from pytest_archon import archrule



def test_rule_basic():

    (

        archrule("name", comment="some comment")

        .match("pytest_archon.col*")

        .exclude("pytest_archon.colgate")

        .should_not_import("pytest_archon.import_finder")

        .should_import("pytest_archon.core*")

        .check("pytest_archon")

    )

```



- To match the modules and constraints,

  [fnmatch](https://docs.python.org/3/library/fnmatch.html) syntax is used (the

  default). You can also use

  [regular expressions](https://docs.python.org/3/library/re.html#regular-expression-syntax)

  by supplying the `use_regex=True` argument to `archrule()`. Example: `archrule(..., use_regex=True).match(...)`.

- `.exclude()` is optional

- `.should_import()` and `.should_not_import()` can be combined and can occur multiple

  times.

- `.may_import()` can be used in combination with `.should_not_import()`.

- `.check()` needs either a module object or a string



The `check()` method can have a few optional parameters, that alter the way the checks

are performed.



- Without parameters, the whole file is checked for imports. So imports done in

  functions and methods are also found. Transitive dependencies are also checked

- Option `only_toplevel_imports=True` will only check for toplevel imports. Conditional

  imports and import in functions and methods are ignored.

- `skip_type_checking=True` will check all imports, but skip imports defined in

  `if typing.TYPE_CHECKING` blocks.

- `only_direct_imports=True` will only check for imports performed by the module

  directly and will not check transitive imports.

- If `only_toplevel_imports=True` is set, `skip_type_checking=True` has no effect.

- Options can be combined.



|                              | Check toplevel imports | Check `TYPE_CHECKING` imports | Check conditional imports, and imports in functions and methods | Check transitive imports |

| ---------------------------- | :--------------------: | :---------------------------: | :-------------------------------------------------------------: | :----------------------: |

| no options enabled           |           ✓            |               ✓               |                                ✓                                |            ✓             |

| `skip_type_checking=True`    |           ✓            |               ✗               |                                ✓                                |            ✓             |

| `only_toplevel_imports=True` |           ✓            |               ✗               |                                ✗                                |            ✓             |

| `only_direct_imports=True`   |           ✓            |               ✓               |                                ✓                                |            ✗             |



## Example



### Domain model has no dependencies



```python

def test_domain():

    # test if the domain model does not import other submodules

    # (the domain model should be standing on its own and be used by other modules)

    (

        archrule("domain", comment="domain does not import any other submodules")

        .match("packageX.domain*") # matches packageX.domain and packageX.domain.*

        .should_not_import("packageX*")

        .may_import("packageX.domain.*")

        .check("packageX")

    )

```



### `util` module is used at more than one place



You can also supply custom constraints as predicate functions.



If you, for example, have a common or util module, you might want to make sure that it

is used at least at two places (otherwise it would not make sense to have a separate

module).



```python

from pytest_archon import archrule



def test_utils_are_shared():

    def have_at_least_two_users(util_module, direct_imports, all_imports):

        # iterate through all imports and find modules using the util_module in question

        users = [k for k, v in all_imports.items() if util_module in v]

        # return True if more than two modules use the util_module

        return len(users) > 2



    archrule("util_is_shared").match("pkg.util").should(have_at_least_two_users).check("pkg")

```



## See also



The blog post [How to tame your Python codebase](https://bargsten.org/wissen/how-to-tame-your-python-codebase/) is also a good overview.



## Similar projects



- [Archunit](https://www.archunit.org/) (Java)

- [Dependency Cruiser](https://github.com/sverweij/dependency-cruiser) (Javascript)

- [import-linter](https://github.com/seddonym/import-linter) (Python)

- [pytestarch](https://pypi.org/project/pytestarch/) (Python)

- [Maintain A Clean Architecture With Dependency Rules - sourcery.ai](https://sourcery.ai/blog/dependency-rules/)

  (Python)

- [GitHub - zyskarch/pytestarch: Test framework for software architecture based on imports between modules.](https://github.com/zyskarch/pytestarch) (Python)