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Generate PlantUML class diagrams to document your Python application.

Project description

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Python to PlantUML

Generate PlantUML class diagrams to document your Python application. status

py2puml uses pre-commit hooks and Continuous Integration to enforce commit messages, code formatting and linting for quality and consistency sake. See the code conventions section if you would like to contribute to the project.

How it works

py2puml produces a class diagram PlantUML script representing classes properties (static and instance attributes) and their relations (composition and inheritance relationships).

py2puml internally uses code inspection (also called reflexion in other programming languages) and abstract tree parsing to retrieve relevant information.

Minimum Python versions to run py2puml

p2puml uses some code-parsing features that are available only since Python 3.8 (like ast.get_source_segment). If your codebase uses the int | float syntax to define optional types, then you should use Python 3.10 to run py2puml.

To sum it up, use at least Python 3.8 to run py2puml, or a higher version if you use syntax features available only in higher versions.

The .python-version file indicates the Python version used to develop the library. It is a file used by pyenv to define the binary used by the project.


From a given path corresponding to a folder containing Python code, py2puml processes each Python module and generates a PlantUML script from the definitions of various data structures using:

  • inspection and type annotations to detect:

    • static class attributes and dataclass fields
    • fields of namedtuples
    • members of enumerations
    • composition and inheritance relationships (between your domain classes only, for documentation sake). The detection of composition relationships relies on type annotations only, assigned values or expressions are never evaluated to prevent unwanted side-effects
  • parsing abstract syntax trees to detect the instance attributes defined in __init__ constructors

py2puml outputs diagrams in PlantUML syntax, which can be:

  • versioned along your code with a unit-test ensuring its consistency (see the's test_py2puml_model_on_py2uml_domain example)
  • generated and hosted along other code documentation (better option: generated documentation should not be versioned with the codebase)

To generate image files, use the PlantUML runtime, a docker image of the runtime (see think/plantuml) or of a server (see the CLI documentation below)

If you like tools related with PlantUML, you may also be interested in this lucsorel/plantuml-file-loader project: a webpack loader which converts PlantUML files into images during the webpack processing (useful to include PlantUML diagrams in your slides with RevealJS or RemarkJS).


Install from PyPI:

  • with pip:
pip install py2puml
poetry add py2puml
pipenv install py2puml



Once py2puml is installed at the system level, an eponymous command is available in your environment shell.

For example, to create the diagram of the classes used by py2puml, run:

py2puml py2puml/domain py2puml.domain

This outputs the following PlantUML content:

@startuml py2puml.domain
namespace py2puml.domain {
  namespace package {}
  namespace umlclass {}
  namespace umlitem {}
  namespace umlenum {}
  namespace umlrelation {}
class py2puml.domain.package.Package {
  name: str
  children: List[Package]
  items_number: int
class py2puml.domain.umlclass.UmlAttribute {
  name: str
  type: str
  static: bool
class py2puml.domain.umlclass.UmlClass {
  attributes: List[UmlAttribute]
  is_abstract: bool
class py2puml.domain.umlitem.UmlItem {
  name: str
  fqn: str
class py2puml.domain.umlenum.Member {
  name: str
  value: str
class py2puml.domain.umlenum.UmlEnum {
  members: List[Member]
enum py2puml.domain.umlrelation.RelType {
  COMPOSITION: * {static}
  INHERITANCE: <| {static}
class py2puml.domain.umlrelation.UmlRelation {
  source_fqn: str
  target_fqn: str
  type: RelType
py2puml.domain.package.Package *-- py2puml.domain.package.Package
py2puml.domain.umlclass.UmlClass *-- py2puml.domain.umlclass.UmlAttribute
py2puml.domain.umlitem.UmlItem <|-- py2puml.domain.umlclass.UmlClass
py2puml.domain.umlenum.UmlEnum *-- py2puml.domain.umlenum.Member
py2puml.domain.umlitem.UmlItem <|-- py2puml.domain.umlenum.UmlEnum
py2puml.domain.umlrelation.UmlRelation *-- py2puml.domain.umlrelation.RelType
footer Generated by //py2puml//

Using PlantUML, this content is rendered as in this diagram:

py2puml domain UML Diagram

For a full overview of the CLI, run:

py2puml --help

The CLI can also be launched as a python module:

python -m py2puml py2puml/domain py2puml.domain

Pipe the result of the CLI with a PlantUML server for instantaneous documentation (rendered by ImageMagick):

# runs a local PlantUML server from a docker container:
docker run -d --rm -p 1234:8080 --name plantumlserver plantuml/plantuml-server:jetty

py2puml py2puml/domain py2puml.domain | curl -X POST --data-binary @- http://localhost:1234/svg/ --output - | display

# stops the container when you don't need it anymore, restarts it later
docker stop plantumlserver
docker start plantumlserver

Python API

For example, to create the diagram of the domain classes used by py2puml:

  • import the py2puml function in your script:
from py2puml.py2puml import py2puml

if __name__ == '__main__':
    # outputs the PlantUML content in the terminal
    print(''.join(py2puml('py2puml/domain', 'py2puml.domain')))

    # writes the PlantUML content in a file
    with open('py2puml/py2puml.domain.puml', 'w', encoding='utf8') as puml_file:
        puml_file.writelines(py2puml('py2puml/domain', 'py2puml.domain'))
  • running it outputs the previous PlantUML diagram in the terminal and writes it in a file.


# directly with poetry
poetry run pytest -v

# in a virtual environment
python3 -m pytest -v

Code coverage (with missed branch statements):

poetry run pytest -v --cov=py2puml --cov-branch --cov-report term-missing --cov-fail-under 93


  • 0.8.0: added support for union types, and github actions (pre-commit hooks + automated tests)
  • 0.7.2: added the current working directory to the import path to make py2puml work in any directory or in native virtual environment (not handled by poetry)
  • 0.7.1: removed obsolete part of documentation: deeply compound types are now well handled (by version 0.7.0)
  • 0.7.0: improved the generated PlantUML documentation (added the namespace structure of the code base, homogenized type between inspection and parsing), improved relationships management (handle forward references, deduplicate relationships)
  • 0.6.1: handle class names with digits
  • 0.6.0: handle abstract classes
  • 0.5.4: fixed the packaging so that the contribution guide is included in the published package
  • 0.5.3: handle constructors decorated by wrapping decorators (decorators making uses of functools.wrap)
  • 0.5.2: specify in pyproject.toml that py2puml requires python 3.8+ (ast.get_source_segment was introduced in 3.8)
  • 0.5.1: prevent from parsing inherited constructors
  • 0.5.0: handle instance attributes in class constructors, add code coverage of unit tests
  • 0.4.0: add a simple CLI
  • 0.3.1: inspect sub-folders recursively
  • 0.3.0: handle classes derived from namedtuples (attribute types are Any)
  • 0.2.0: handle inheritance relationships and enums
  • 0.1.3: first release, handle all modules of a folder and compositions of domain classes


Unless stated otherwise all works are licensed under the MIT license, a copy of which is included here.


Pull requests

Pull-requests are welcome and will be processed on a best-effort basis.

Pull requests must follow the guidelines enforced by the pre-commit hooks:

  • commit messages must follow the Angular conventions enforced by the commitlint hook
  • code formatting must follow the conventions enforced by the isort and yapf hooks
  • code linting should not detect code smells in your contributions, this is checked by the ruff hook

Please also follow the contributing guide to ease your contribution.

Code conventions

The code conventions are described and enforced by pre-commit hooks to maintain consistency across the code base. The hooks are declared in the .pre-commit-config.yaml file.

Set the git hooks (pre-commit and commit-msg types):

poetry run pre-commit install --hook-type pre-commit --hook-type commit-msg

Before committing, you can check your changes with:

# put all your changes in the git staging area
git add -A

# all hooks
poetry run pre-commit run --all-files

# a specific hook
poetry run pre-commit run ruff --all-files

Commit messages

Please, follow the conventions of the Angular team for commit messages. When merging your pull-request, the new version of the project will be derived from the messages.

Code formatting

This project uses isort and yapf to format the code. The guidelines are expressed in their respective sections in the pyproject.toml file.

Best practices

This project uses the ruff linter, which is configured in its section in the pyproject.toml file.

Current limitations

  • regarding inspection

    • type hinting is optional when writing Python code and discarded when it is executed, as mentionned in the typing official documentation. The quality of the diagram output by py2puml depends on the reliability with which the type annotations were written

    The Python runtime does not enforce function and variable type annotations. They can be used by third party tools such as type checkers, IDEs, linters, etc.

  • regarding the detection of instance attributes with AST parsing:

    • only constructors are visited, attributes assigned in other functions won't be documented
    • attribute types are inferred from type annotations:
      • of the attribute itself
      • of the variable assigned to the attribute: a signature parameter or a locale variable
      • to avoid side-effects, no code is executed nor interpreted


If py2puml does not meet your needs (suggestions and pull-requests are welcome), you can have a look at these projects which follow other approaches (AST, linting, modeling):

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