Add ruff Python linter

flake.nix

@@ -33,12 +33,13 @@
 
         devShells.default = pkgs.mkShell {
           packages = [
-            pkgs.treefmt
-            pkgs.deadnix
-            pkgs.statix
-            pkgs.nixpkgs-fmt
+            pkgs.treefmt # Format all the things in one go
+            pkgs.deadnix # Check for dead Nix code
+            pkgs.statix # Static Nix analysis
+            pkgs.ruff # Python linter
+            pkgs.nixpkgs-fmt # Nix formatter
             pythonEnv
-            pkgs.pdm
+            pkgs.pdm # Python PEP-621 compliant package manager
           ];
 
           shellHook = ''
@@ -72,6 +73,7 @@
             deadnix = "deadnix --fail";
             statix = "statix check";
             mypy = "mypy .";
+            ruff = "ruff check .";
           };
 
       });

pyproject.toml

@@ -21,3 +21,26 @@ dev = [
     "black>=23.7.0",
     "mypy>=1.4.1",
 ]
+
+[tool.black]
+line-length = 120
+target-version = ["py37", "py38", "py39", "py310"]
+
+[tool.ruff]
+line-length = 120
+extend-select = [
+  "I",    # isort
+  "B",    # flake8-bugbear
+  "C4",   # flake8-comprehensions
+  "PGH",  # pygrep-hooks
+  "RUF",  # ruff
+  "W",    # pycodestyle
+  "YTT",  # flake8-2020
+]
+extend-ignore = ["B018", "B019"]
+src = ["src"]
+exclude = ["tests/fixtures"]
+target-version = "py37"
+
+[tool.ruff.mccabe]
+max-complexity = 10

tests/test_nix.py

@@ -1,15 +1,16 @@
+import json
+import subprocess
 from typing import (
-    Iterator,
-    Optional,
+    Any,
     Dict,
+    Iterator,
     List,
-    cast,
+    Optional,
     Set,
-    Any,
+    cast,
 )
-import subprocess
+
 import pytest
-import json
 
 
 def assert_deepequals(
@@ -37,13 +38,13 @@ def assert_deepequals(
     }, ignore_paths=set(["metadata.poetry-version"]))
     """
 
-    _path = cast(tuple[str], (_path if _path else tuple()))
+    _path = cast(tuple[str], (_path if _path else ()))
     ignore_paths = ignore_paths if ignore_paths else set()
     path = ".".join(_path)
     err = ValueError("{}: {} != {}".format(path, a, b))
 
     def make_path(entry):
-        return _path + (str(entry),)
+        return (*_path, str(entry))
 
     if isinstance(a, list):
         if not isinstance(b, list) or len(a) != len(b):
@@ -82,9 +83,7 @@ def nix_eval(attr: str) -> Dict:
         "-A",
         attr,
     ]
-    proc = subprocess.run(
-        cmd, stdout=subprocess.PIPE, check=True, stderr=subprocess.PIPE
-    )
+    proc = subprocess.run(cmd, stdout=subprocess.PIPE, check=True, stderr=subprocess.PIPE)
     return json.loads(proc.stdout)