🎉 run code quality checks automatically

* installs black and flake8 as pre-commit hooks
* runs only on modified files

.pre-commit-config.yaml

@@ -0,0 +1,10 @@
+repos:
+-   repo: https://github.com/ambv/black
+    rev: 21.6b0
+    hooks:
+    - id: black
+      language_version: python3.7
+-   repo: https://gitlab.com/pycqa/flake8
+    rev: 3.9.2
+    hooks:
+    - id: flake8

CONTRIBUTING.md

@@ -177,6 +177,15 @@ tools installed.
 **⚠️ Note that formatting and linting is currently only possible for Python
 modules in `.py` files, not Cython modules in `.pyx` and `.pxd` files.**
 
+### Pre-Commit Hooks
+
+After cloning the repo, after installing the packages from `requirements.txt`, enter the repo folder and run `pre-commit install`.
+Each time a `git commit` is initiated, `black` and `flake8` will run automatically on the modified files only.
+
+In case of error, or when `black` modified a file, the modified file needs to be `git add` once again and a new
+`git commit` has to be issued.
+
+
 ### Code formatting
 
 [`black`](https://github.com/ambv/black) is an opinionated Python code

requirements.txt

@@ -22,6 +22,7 @@ setuptools
 packaging>=20.0
 typing_extensions>=3.7.4.1,<4.0.0.0; python_version < "3.8"
 # Development dependencies
+pre-commit>=2.13.0
 cython>=0.25,<3.0
 pytest>=5.2.0
 pytest-timeout>=1.3.0,<2.0.0