support 'append_delimiter' to fix #1679

alembic/command.py

@@ -152,6 +152,7 @@ def init(
                     file_path,
                     toml_path,
                     script_location=toml_script_location_directory,
+                    append_delimiter=b"\n\n",
                 )
             else:
                 script._generate_template(

alembic/util/pyfiles.py

@@ -27,6 +27,7 @@ def template_to_file(
     output_encoding: str,
     *,
     append: bool = False,
+    append_delimiter: Optional[bytes] = None,
     **kw: Any,
 ) -> None:
     template = Template(filename=_preserving_path_as_str(template_file))
@@ -45,6 +46,12 @@ def template_to_file(
             "template-oriented traceback." % fname
         )
     else:
+        if append and append_delimiter:
+            if os.path.exists(dest):
+                with open(dest, "rb") as f:
+                    _exsiting = f.read()
+                    if not _exsiting.endswith(append_delimiter):
+                        output = append_delimiter + output
         with open(dest, "ab" if append else "wb") as f:
             f.write(output)