fix: improve changelog script

 - fixed issue when no commits between tags
 - added Python version check to start of script
 - use python3 env (maybe not the most portable?)

Author: steabert

.gitignore

@@ -18,3 +18,5 @@ yarn-error.log*
 .DS_Store
 
 .env
+
+__pycache__/

sbin/changelog.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import argparse
 import re
@@ -7,6 +7,15 @@
 
 import utils
 
+#
+# Stop immediately if version too old.
+#
+_MINIMUM_PYTHON_VERSION = "3.7"
+if sys.version_info < tuple(map(int, _MINIMUM_PYTHON_VERSION.split("."))):
+    raise Exception(
+        f"You need Python >= {_MINIMUM_PYTHON_VERSION}, but you are running {sys.version}"
+    )
+
 GITHUB_COMPARE_URL = (
     "https://github.com/AxisCommunications/practical-react-components/compare"
 )
@@ -37,6 +46,9 @@ def changelog_part(commitish_to: str, commitish_from: str, version: str):
         ["git", "log", "--no-merges", "--date-order", "--format=%H%x09%s", commit_range]
     )
 
+    if commits == "":
+        return ""
+
     messages = {}
 
     for commit in commits.split("\n"):