Remove py2 exception handeling and move file to dj4 standard (#6131)

* remove py2 exception handeling and move file to dj4 standard

* re-add coverage exception

InvenTree/manage.py

@@ -1,23 +1,23 @@
+#!/usr/bin/env python
 """InvenTree / django management commands"""
 
 import os
 import sys
 
-if __name__ == "__main__":
+
+def main():
+    """Run administrative tasks."""
     os.environ.setdefault("DJANGO_SETTINGS_MODULE", "InvenTree.settings")
     try:
         from django.core.management import execute_from_command_line
-    except ImportError:  # pragma: no cover
-        # The above import may fail for some other reason. Ensure that the
-        # issue is really that Django is missing to avoid masking other
-        # exceptions on Python 2.
-        try:
-            import django  # noqa: F401
-        except ImportError:
-            raise ImportError(
-                "Couldn't import Django. Are you sure it's installed and "
-                "available on your PYTHONPATH environment variable? Did you "
-                "forget to activate a virtual environment?"
-            )
-        raise
+    except ImportError as exc:  # pragma: no cover
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
     execute_from_command_line(sys.argv)
+
+
+if __name__ == "__main__":
+    main()