Fix python 3.8/3.9 compat

Author: virtuald

src/semiwrap/hooks.py

@@ -69,17 +69,16 @@ def initialize(self, version: str, build_data: T.Dict[str, T.Any]) -> None:
                 raise
 
             msg = [
-                "ERROR: exception occurred when processing `pyproject.toml`",
-                "",
+                "ERROR: exception occurred when processing `pyproject.toml`\n\n",
             ]
 
-            msg += traceback.format_exception_only(e)
+            msg += traceback.format_exception_only(type(e), e)
             cause = e.__context__
             while cause is not None:
                 if "prepare_metadata_for_build_editable" in str(cause):
                     break
 
-                el = traceback.format_exception_only(cause)
+                el = traceback.format_exception_only(type(cause), cause)
                 el[0] = f"- caused by {el[0]}"
                 msg += el
 
@@ -89,10 +88,10 @@ def initialize(self, version: str, build_data: T.Dict[str, T.Any]) -> None:
                 cause = cause.__context__
 
             msg.append(
-                "Set environment variable SEMIWRAP_ERROR_VERBOSE=1 for stacktrace"
+                "\nSet environment variable SEMIWRAP_ERROR_VERBOSE=1 for stacktrace"
             )
 
-            print("\n".join(msg), file=sys.stderr)
+            print("".join(msg), file=sys.stderr)
             sys.exit(1)
 
         if eps: