build(deps): Add back black

ruff doesn't replace black, yet

Makefile

@@ -30,6 +30,9 @@ start_docs:
 design_docs:
 	$(MAKE) -C docs design
 
+black:
+	poetry run black `${PY_FILES}`
+
 ruff:
 	ruff .
 

docs/developing.md

@@ -48,6 +48,36 @@ Rebuild docs and run server via one terminal: `make dev_docs` (requires above, a
 
 ## Formatting / Linting
 
+### black
+
+[black] is used for formatting.
+
+````{tab} Command
+
+poetry:
+
+```console
+$ poetry run black .
+```
+
+If you setup manually:
+
+```console
+$ black .
+```
+
+````
+
+````{tab} make
+
+```console
+$ make black
+```
+
+````
+
+In the future, `ruff` (below) may replace black as formatter.
+
 ### ruff
 
 The project uses [ruff] to handles formatting, sorting imports and linting.
@@ -156,5 +186,6 @@ Update `__version__` in `src/gp_libs.py` and `pyproject.toml`::
 [poetry]: https://python-poetry.org/
 [entr(1)]: http://eradman.com/entrproject/
 [`entr(1)`]: http://eradman.com/entrproject/
+[black]: https://github.com/psf/black
 [ruff]: https://ruff.rs
 [mypy]: https://mypy-lang.org/

pyproject.toml

@@ -66,6 +66,7 @@ coverage = "*"
 pytest-cov = "*"
 
 ### Lint ###
+black = "*"
 ruff = "*"
 mypy = "*"
 typing-extensions = { version = "*", python = "^3.7" }
@@ -85,6 +86,7 @@ docs = [
 test = ["pytest", "pytest-rerunfailures", "pytest-watcher"]
 coverage = ["codecov", "coverage", "pytest-cov"]
 lint = [
+  "black",
   "ruff",
   "mypy",
   "types-docutils",