3.1.0 and up require pydot

[danhorner]

When I upgrade from 3.0.0 to 3.1.0, importing a module that defines a StateChart subclass railse with ModuleNotFoundError: No module named pydot during the class definition. This happens at import before any of my user code runs. I think something changed with the new documentation features that makes pydot a hard dependency instead of optional on the [diagrams] extra.

Does this track? I can investigate farther if helpful.

  src/app_fsm/my_state_machine.py:176: in <module>
      class MyStateMachine(MyStateChart):
  .venv/.../statemachine/factory.py:95: in __init__
      cls._expand_docstring()
  .venv/.../statemachine/factory.py:105: in _expand_docstring
      from .contrib.diagram.formatter import formatter
  .venv/.../statemachine/contrib/diagram/__init__.py:7: in <module>
      from .renderers.dot import DotRenderer
  .venv/.../statemachine/contrib/diagram/renderers/dot.py:9: in <module>
      import pydot
  E   ModuleNotFoundError: No module named 'pydot'

Thanks for your work on this project!

[fgmacedo]

Hi @danhorner, thanks for the clear bug report and the precise traceback — it pointed straight at the root cause.

This is fixed in v3.1.2, just released to PyPI: https://pypi.org/project/python-statemachine/3.1.2/

Two changes restore the original behavior:

• _expand_docstring (called by the metaclass for every subclass) now short-circuits when the docstring has no {statechart:FORMAT} placeholder, skipping the formatter import for the common case.
• statemachine.contrib.diagram no longer re-exports renderer classes at the package top level, and the renderer modules are only imported when actually used. pydot is now only required when rendering dot/svg. Mermaid and Markdown/RST work without it.

If your code happened to import DotRenderer/MermaidRenderer (or their *Config) from statemachine.contrib.diagram directly, import them from the renderer submodule instead:

from statemachine.contrib.diagram.renderers.dot import DotRenderer
from statemachine.contrib.diagram.renderers.mermaid import MermaidRenderer

Release notes: https://github.com/fgmacedo/python-statemachine/releases/tag/v3.1.2

Thanks again for taking the time to file this!

[danhorner]

Thanks for the quick fix!