ArchUnitPython - Architecture Testing

Enforce architecture rules in Python projects. Check for dependency directions, detect circular dependencies, enforce coding standards and much more. Integrates with pytest and any other testing framework. Very simple setup and pipeline integration. Zero runtime dependencies.

Inspired by the amazing ArchUnit library but we are not affiliated with ArchUnit.

Setup • Use Cases • Features • Contributing

⚡ 5 min Quickstart

Installation

pip install archunitpython

Add tests

Simply add tests to your existing test suites. The following is an example using pytest. First we ensure that we have no circular dependencies.

from archunitpython import project_files, metrics, assert_passes

def test_no_circular_dependencies():
    rule = project_files("src/").in_folder("src/**").should().have_no_cycles()
    assert_passes(rule)

Next we ensure that our layered architecture is respected.

def test_presentation_should_not_depend_on_database():
    rule = (
        project_files("src/")
        .in_folder("**/presentation/**")
        .should_not()
        .depend_on_files()
        .in_folder("**/database/**")
    )
    assert_passes(rule)

def test_business_should_not_depend_on_database():
    rule = (
        project_files("src/")
        .in_folder("**/business/**")
        .should_not()
        .depend_on_files()
        .in_folder("**/database/**")
    )
    assert_passes(rule)

# More layers ...

Lastly we ensure that some code metric rules are met.

def test_no_large_files():
    rule = metrics("src/").count().lines_of_code().should_be_below(1000)
    assert_passes(rule)

def test_high_cohesion():
    # LCOM metric (lack of cohesion of methods), low = high cohesion
    rule = metrics("src/").lcom().lcom96b().should_be_below(0.3)
    assert_passes(rule)

CI Integration

These tests run automatically in your testing setup, for example in your CI pipeline, so that's basically it. This setup ensures that the architectural rules you have defined are always adhered to!

# GitHub Actions
- name: Run Architecture Tests
  run: pytest tests/test_architecture.py -v

🚐 Setup

Installation:

pip install archunitpython

That's it. Works with pytest, unittest, or any Python testing framework.

pytest (Recommended)

Use assert_passes() for clean assertion messages:

from archunitpython import project_files, assert_passes

def test_my_architecture():
    rule = project_files("src/").should().have_no_cycles()
    assert_passes(rule)

Any Other Framework

Use .check() directly and assert on the violations list:

from archunitpython import project_files

rule = project_files("src/").should().have_no_cycles()
violations = rule.check()
assert len(violations) == 0

Configuration Options

Both assert_passes() and .check() accept configuration options:

from archunitpython import CheckOptions

options = CheckOptions(
    allow_empty_tests=True,  # Don't fail when no files match
    clear_cache=True,        # Clear the graph cache
)

violations = rule.check(options)

🐹 Use Cases

Here is an overview of common use cases.

Layered Architecture:

Enforce that higher layers don't depend on lower layers and vice versa.

Clean Architecture / Hexagonal:

Validate that domain logic doesn't depend on infrastructure.

Microservices / Modular:

Ensure services/modules don't have forbidden cross-dependencies.

🐲 Example Repository

Here is a repository with a fully functioning example that uses ArchUnitPython to ensure architectural rules:

• RAG Pipeline Test Showcase: A test showcase demonstrating ArchUnitPython's architecture testing capabilities on a RAG pipeline

🐣 Features

This is an overview of what you can do with ArchUnitPython.

Circular Dependencies

def test_services_cycle_free():
    rule = project_files("src/").in_folder("**/services/**").should().have_no_cycles()
    assert_passes(rule)

Layer Dependencies

def test_clean_architecture_layers():
    rule = (
        project_files("src/")
        .in_folder("**/presentation/**")
        .should_not()
        .depend_on_files()
        .in_folder("**/database/**")
    )
    assert_passes(rule)

def test_business_not_depend_on_presentation():
    rule = (
        project_files("src/")
        .in_folder("**/business/**")
        .should_not()
        .depend_on_files()
        .in_folder("**/presentation/**")
    )
    assert_passes(rule)

Naming Conventions

def test_naming_patterns():
    rule = (
        project_files("src/")
        .in_folder("**/services/**")
        .should()
        .have_name("*_service.py")
    )
    assert_passes(rule)

Code Metrics

def test_no_large_files():
    rule = metrics("src/").count().lines_of_code().should_be_below(1000)
    assert_passes(rule)

def test_high_class_cohesion():
    rule = metrics("src/").lcom().lcom96b().should_be_below(0.3)
    assert_passes(rule)

def test_method_count():
    rule = metrics("src/").count().method_count().should_be_below(20)
    assert_passes(rule)

def test_field_count_for_data_classes():
    rule = (
        metrics("src/")
        .for_classes_matching("*Data*")
        .count()
        .field_count()
        .should_be(3)
    )
    assert_passes(rule)

Distance Metrics

def test_proper_coupling():
    rule = metrics("src/").distance().distance_from_main_sequence().should_be_below(0.3)
    assert_passes(rule)

def test_not_in_zone_of_pain():
    rule = metrics("src/").distance().not_in_zone_of_pain()
    assert_passes(rule)

Custom Rules

You can define your own custom rules.

rule_desc = "Python files should have docstrings"

def has_docstring(file):
    return '"""' in file.content or "'''" in file.content

violations = (
    project_files("src/")
    .with_name("*.py")
    .should()
    .adhere_to(has_docstring, rule_desc)
    .check()
)

assert len(violations) == 0

Custom Metrics

You can define your own metrics as well.

def test_method_field_ratio():
    rule = (
        metrics("src/")
        .custom_metric(
            "methodFieldRatio",
            "Ratio of methods to fields",
            lambda ci: len(ci.methods) / max(len(ci.fields), 1),
        )
        .should_be_below(10)
    )
    assert_passes(rule)

Architecture Slices

import re
from archunitpython import project_slices

def test_adhere_to_diagram():
    diagram = """
@startuml
  component [controllers]
  component [services]
  [controllers] --> [services]
@enduml"""

    rule = (
        project_slices("src/")
        .defined_by_regex(re.compile(r"/([^/]+)/[^/]+\.py$"))
        .should()
        .adhere_to_diagram(diagram)
    )
    assert_passes(rule)

def test_no_forbidden_dependency():
    rule = (
        project_slices("src/")
        .defined_by("src/(**)/**")
        .should_not()
        .contain_dependency("services", "controllers")
    )
    assert_passes(rule)

Reports

Generate HTML reports for your metrics. Note that this feature is in beta.

from archunitpython.metrics.fluentapi.export_utils import MetricsExporter, ExportOptions

MetricsExporter.export_as_html(
    {"MethodCount": 5, "FieldCount": 3, "LinesOfCode": 150},
    ExportOptions(
        output_path="reports/metrics.html",
        title="Architecture Metrics Dashboard",
    ),
)

🔎 Pattern Matching System

We offer three targeting options for pattern matching across all modules:

• with_name(pattern) - Pattern is checked against the filename (e.g. service.py from src/services/service.py)
• in_path(pattern) - Pattern is checked against the full relative path (e.g. src/services/service.py)
• in_folder(pattern) - Pattern is checked against the path without filename (e.g. src/services from src/services/service.py)

For the metrics module there is an additional one:

• for_classes_matching(pattern) - Pattern is checked against class names. The filepath or filename does not matter here

Pattern Types

We support string patterns and regular expressions. String patterns support glob.

# String patterns with glob support (case sensitive)
.with_name("*_service.py")       # All files ending with _service.py
.in_folder("**/services")        # All files in any services folder
.in_path("src/api/**/*.py")      # All Python files under src/api

# Regular expressions
import re
.with_name(re.compile(r".*Service\.py$"))
.in_folder(re.compile(r"services$"))

# For metrics module: Class name matching
.for_classes_matching("*Service*")
.for_classes_matching(re.compile(r"^User.*"))

Glob Patterns Guide

Basic Wildcards

• * - Matches any characters within a single path segment (except /)
• ** - Matches any characters across multiple path segments
• ? - Matches exactly one character

Common Glob Examples

# Filename patterns
.with_name("*.py")              # All Python files
.with_name("*_service.py")      # Files ending with _service.py
.with_name("test_*.py")         # Files starting with test_

# Folder patterns
.in_folder("**/services")       # Any services folder at any depth
.in_folder("src/services")      # Exact src/services folder
.in_folder("**/test/**")        # Any folder containing test in path

# Path patterns
.in_path("src/**/*.py")                # Python files anywhere under src
.in_path("**/test/**/*_test.py")       # Test files in any test folder

Recommendation

We generally recommend using string patterns with glob support unless you need very special cases. Regular expressions add extra complexity that is not necessary for most cases.

Supported Metric Types

LCOM (Lack of Cohesion of Methods)

The LCOM metrics measure how well the methods and fields of a class are connected. Lower values indicate better cohesion.

# LCOM96a (Henderson et al.)
metrics("src/").lcom().lcom96a().should_be_below(0.8)

# LCOM96b (Henderson et al.) - most commonly used
metrics("src/").lcom().lcom96b().should_be_below(0.7)

All 8 LCOM variants are available: lcom96a(), lcom96b(), lcom1() through lcom5(), and lcomstar().

The LCOM96b metric is calculated as:

LCOM96b = (1/a) * sum((1/m) * (m - mu(Ai)))

Where:

• m is the number of methods in the class
• a is the number of attributes (fields) in the class
• mu(Ai) is the number of methods that access attribute Ai

The result is a value between 0 and 1:

• 0: perfect cohesion (all methods access all attributes)
• 1: complete lack of cohesion (each method accesses its own attribute)

Count Metrics

metrics("src/").count().method_count().should_be_below(20)
metrics("src/").count().field_count().should_be_below(15)
metrics("src/").count().lines_of_code().should_be_below(200)
metrics("src/").count().statements().should_be_below(100)
metrics("src/").count().imports().should_be_below(20)

Distance Metrics

metrics("src/").distance().abstractness().should_be_above(0.3)
metrics("src/").distance().instability().should_be_below(0.8)
metrics("src/").distance().distance_from_main_sequence().should_be_below(0.5)

Custom Metrics

metrics("src/").custom_metric(
    "complexityRatio",
    "Ratio of methods to fields",
    lambda ci: len(ci.methods) / max(len(ci.fields), 1),
).should_be_below(3.0)

📐 UML Diagram Support

ArchUnitPython can validate your architecture against PlantUML diagrams, ensuring your code matches your architectural designs.

Component Diagrams

def test_component_architecture():
    diagram = """
@startuml
component [UserInterface]
component [BusinessLogic]
component [DataAccess]

[UserInterface] --> [BusinessLogic]
[BusinessLogic] --> [DataAccess]
@enduml"""

    rule = (
        project_slices("src/")
        .defined_by("src/(**)/**")
        .should()
        .adhere_to_diagram(diagram)
    )
    assert_passes(rule)

Diagram from File

def test_from_file():
    rule = (
        project_slices("src/")
        .defined_by("src/(**)/**")
        .should()
        .adhere_to_diagram_in_file("docs/architecture.puml")
    )
    assert_passes(rule)

📢 Informative Error Messages

When tests fail, you get helpful output with file paths and violation details:

Found 2 architecture violation(s):

  1. File dependency violation
     'src/api/bad_shortcut.py' depends on 'src/retrieval/vector_store.py'

  2. File dependency violation
     'src/api/bad_shortcut.py' depends on 'src/retrieval/embedder.py'

📝 Debug Logging & Configuration

We support logging to help you understand what files are being analyzed and troubleshoot test failures. Logging is disabled by default to keep test output clean.

Enabling Debug Logging

from archunitpython import CheckOptions
from archunitpython.common.logging.types import LoggingOptions

options = CheckOptions(
    logging=LoggingOptions(
        enabled=True,
        level="debug",       # "error" | "warn" | "info" | "debug"
        log_file=True,       # Creates logs/archunit-YYYY-MM-DD_HH-MM-SS.log
    ),
)

violations = rule.check(options)

CI Pipeline Integration

# GitHub Actions
- name: Run Architecture Tests
  run: pytest tests/test_architecture.py -v

- name: Upload Test Logs
  if: always()
  uses: actions/upload-artifact@v3
  with:
    name: architecture-test-logs
    path: logs/

🏈 Architecture Fitness Functions

The features of ArchUnitPython can very well be used as architectural fitness functions. See here for more information about that topic.

🔲 Core Modules

ArchUnitPython uses ArchUnitPython

We use ourselves to ensure the architectural rules for this repository.

🦊 Contributing

We highly appreciate contributions. We use GitHub Flow, meaning that we use feature branches. As soon as something is merged or pushed to main it gets deployed. Versioning is automated via Conventional Commits. See more in Contributing.

ℹ️ FAQ

Q: What Python testing frameworks are supported?

ArchUnitPython works with pytest, unittest, and any other testing framework. We recommend pytest with assert_passes().

Q: What Python versions are supported?

Python 3.10 and above.

Q: Does ArchUnitPython have any runtime dependencies?

No. ArchUnitPython uses only the Python standard library. Development dependencies (pytest, mypy, ruff) are optional.

Q: How does it analyze Python imports?

ArchUnitPython uses Python's built-in ast module to parse source files and resolve imports. It handles absolute imports, relative imports, and package imports.

Q: How do I handle false positives in architecture rules?

Use the filtering and targeting capabilities to exclude specific files or patterns. You can filter by file paths, class names, or custom predicates to fine-tune your rules.

📅 Plans

ArchUnitPython is the Python port of ArchUnitTS. We plan to keep it in sync with the TypeScript version's features, and extend it with Python-specific capabilities.

🐣 Origin Story

ArchUnitPython started as the Python port of ArchUnitTS. With the rise of LLMs and AI integration, enforcing architectural boundaries and QA in general has become more critical than ever -- especially in Python, the dominant language in the AI/ML ecosystem.

💟 Community

Maintainers

• LukasNiessen - Creator and main maintainer

Contributors

Questions

Found a bug? Want to discuss features?

• Submit an issue on GitHub
• Join our GitHub Discussions

If ArchUnitPython helps your project, please consider:

• Starring the repository 💚
• Suggesting new features 💭
• Contributing code or documentation ⌨️

Star History

📄 License

This project is under the MIT license.

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