Switched to ruff

Author: forman

.flake8

@@ -20,7 +20,9 @@ checklist are addressed in your PR.
 
 **PR checklist**
 
-* Format code using [black](https://black.readthedocs.io/) with default settings.
+* Format code using first [isort](https://pycqa.github.io/isort/) 
+  then [ruff](https://black.readthedocs.io/) with default settings
+  (`ruff format .`).
   Check also section [code style](#code-style) below.
 * Your change shall not break existing unit tests.
   `pytest` must run without errors.
@@ -38,10 +40,9 @@ checklist are addressed in your PR.
 ## Code style
 
 The `zappend` code compliant to [PEP-8](https://pep8.org/) except for a line 
-length of 88 characters as recommended by [black](https://black.readthedocs.io/).
-Since black is un-opinionated regarding the order of imports, 
-we use the following three import blocks separated by an empty 
-line:
+length of 88 characters as used by `ruff format`.
+We structure imports using three blocks separated by an empty 
+line and sort them using `isort` _before_ applying `ruff`:
 
 1. Python standard library imports, e.g., `os`, `typing`, etc
 2. 3rd-party imports, e.g., `xarray`, `zarr`, etc

CONTRIBUTING.md

@@ -9,7 +9,7 @@
 [![codecov](https://codecov.io/gh/bcdev/zappend/graph/badge.svg?token=B3R6bNmAUp)](https://codecov.io/gh/bcdev/zappend)
 [![PyPI Version](https://img.shields.io/pypi/v/zappend)](https://pypi.org/project/zappend/)
 [![Conda Version](https://anaconda.org/conda-forge/zappend/badges/version.svg)](https://anaconda.org/conda-forge/zappend)
-[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)
+[![Ruff](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/charliermarsh/ruff/main/assets/badge/v0.json)](https://github.com/charliermarsh/ruff)
 [![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/bcdev/zappend/HEAD?labpath=examples%2Fzappend-demo.ipynb)
 [![GitHub License](https://img.shields.io/github/license/bcdev/zappend)](https://github.com/bcdev/zappend)
 

README.md

@@ -45,10 +45,11 @@ pytest --cov=zappend tests
 
 ### Code Style
 
-`zappend` source code is formatted using the [black](https://black.readthedocs.io/) tool.
+`zappend` source code is formatted using the 
+[ruff](https://github.com/charliermarsh/ruff) tool.
 
 ```bash
-black zappend
+ruff format .
 ```
 
 ### Documentation