Excluded black from dev for Python 3.7

We excluded black from development dependencies for Python 3.7 as black
dropped support for Python 3.7 (due to its EOL) and only supports Python
versions from 3.8 on.

precommit.py

@@ -23,34 +23,42 @@ def main() -> int:
 
     repo_root = pathlib.Path(__file__).parent
 
-    print("Reformatting...")
-    reformat_targets = [
-        "tests",
-        "icontract",
-        "setup.py",
-        "precommit.py",
-        "benchmark.py",
-        "benchmarks",
-        "tests_with_others",
-    ]
-
-    if sys.version_info >= (3, 6):
-        reformat_targets.append("tests_3_6")
-
-    if sys.version_info >= (3, 7):
-        reformat_targets.append("tests_3_7")
-
-    if sys.version_info >= (3, 8, 5):
-        reformat_targets.append("tests_3_8")
-
-    if overwrite:
-        subprocess.check_call(
-            [sys.executable, "-m", "black"] + reformat_targets, cwd=str(repo_root)
+    if sys.version_info < (3, 8):
+        print(
+            "Our formatter, black, supports only Python versions from 3.8 on. "
+            "However, you are running Python {}. Hence, the reformatting step "
+            "will be skipped.".format(sys.version_info)
         )
     else:
-        subprocess.check_call(
-            [sys.executable, "-m", "black"] + reformat_targets, cwd=str(repo_root)
-        )
+        print("Reformatting...")
+
+        reformat_targets = [
+            "tests",
+            "icontract",
+            "setup.py",
+            "precommit.py",
+            "benchmark.py",
+            "benchmarks",
+            "tests_with_others",
+        ]
+
+        if sys.version_info >= (3, 6):
+            reformat_targets.append("tests_3_6")
+
+        if sys.version_info >= (3, 7):
+            reformat_targets.append("tests_3_7")
+
+        if sys.version_info >= (3, 8, 5):
+            reformat_targets.append("tests_3_8")
+
+        if overwrite:
+            subprocess.check_call(
+                [sys.executable, "-m", "black"] + reformat_targets, cwd=str(repo_root)
+            )
+        else:
+            subprocess.check_call(
+                [sys.executable, "-m", "black"] + reformat_targets, cwd=str(repo_root)
+            )
 
     if sys.version_info < (3, 8):
         print(

setup.py

@@ -52,7 +52,6 @@
     extras_require={
         "dev": [
             "pylint==2.13.9",
-            "black==23.9.1",
             "tox>=3.0.0",
             "pydocstyle>=6.1.1,<7",
             "coverage>=4.5.1,<5",
@@ -66,6 +65,7 @@
             "numpy>=1,<2",
         ]
         + (["mypy==1.5.1"] if sys.version_info >= (3, 8) else [])
+        + (["black==23.9.1"] if sys.version_info >= (3, 8) else [])
         + (["deal==4.23.3"] if sys.version_info >= (3, 8) else [])
         + (["asyncstdlib==3.9.1"] if sys.version_info >= (3, 8) else []),
     },