diff --git a/src/glue/jobs/s3_to_json.py b/src/glue/jobs/s3_to_json.py
index 7decb52..0e3002e 100644
--- a/src/glue/jobs/s3_to_json.py
+++ b/src/glue/jobs/s3_to_json.py
@@ -526,13 +526,14 @@ def write_file_to_json_dataset(
     Returns:
         list: A list of files uploaded to S3
     """
-    # Configuration related to where we write our part files
+    # Configuration related to where we write the JSON
     output_dir = os.path.join(
         f"dataset={metadata['type']}", f"cohort={metadata['cohort']}"
     )
     os.makedirs(output_dir, exist_ok=True)
     part_number = 0
-    part_output_path = get_output_path(
+    # we update this value as we write
+    current_part_path = get_output_path(
         metadata=metadata, part_number=part_number, output_dir=output_dir, touch=True
     )
     compressed_output_path = get_output_path(
@@ -541,75 +542,75 @@ def write_file_to_json_dataset(
 
     # We will attach file metadata to the uploaded S3 object
     s3_metadata = _derive_str_metadata(metadata=metadata)
+    line_count = 0
     uploaded_files = []
-    with z.open(json_path, "r") as input_json:
-        with gzip.open(
-            compressed_output_path, "wt", encoding="utf-8"
-        ) as f_compressed_out:
-            current_part_path = part_output_path
-            line_count = 0
-            for transformed_block in transform_block(
-                input_json=input_json, metadata=metadata, logger_context=logger_context
-            ):
-                current_file_size = os.path.getsize(current_part_path)
-                if current_file_size > file_size_limit:
-                    # Upload completed part file
-                    _upload_file_to_json_dataset(
-                        file_path=current_part_path,
-                        s3_metadata=s3_metadata,
-                        workflow_run_properties=workflow_run_properties,
-                        delete_upon_successful_upload=delete_upon_successful_upload,
-                    )
-                    uploaded_files.append(current_part_path)
-                    # Update output path to next part
-                    part_number += 1
-                    current_part_path = get_output_path(
-                        metadata=metadata,
-                        part_number=part_number,
-                        output_dir=output_dir,
-                        touch=True,
-                    )
-                # Write block data to both part file and compressed file
-                for transformed_record in transformed_block:
-                    line_count += 1
-                    record_with_newline = "{}\n".format(json.dumps(transformed_record))
-                    with open(current_part_path, "a") as f_out:
-                        f_out.write(record_with_newline)
-                    f_compressed_out.write(record_with_newline)
-            # Upload final block
-            _upload_file_to_json_dataset(
-                file_path=current_part_path,
-                s3_metadata=s3_metadata,
-                workflow_run_properties=workflow_run_properties,
-                delete_upon_successful_upload=delete_upon_successful_upload,
-            )
-            uploaded_files.append(current_part_path)
-            logger_extra = dict(
-                merge_dicts(
-                    logger_context,
-                    {
-                        "file.LineCount": line_count,
-                        "event.kind": "metric",
-                        "event.category": ["file"],
-                        "event.type": ["info", "creation"],
-                        "event.action": "list-file-properties",
-                        "labels": {
-                            k: v.isoformat() if isinstance(v, datetime.datetime) else v
-                            for k, v in metadata.items()
-                        },
-                    },
+    # fmt: off
+    # <python3.10 requires this backslash syntax, we currently run 3.7
+    with z.open(json_path, "r") as input_json, \
+         open(current_part_path, "a") as f_out, \
+         gzip.open(compressed_output_path, "wt", encoding="utf-8") as f_compressed_out:
+        for transformed_block in transform_block(
+            input_json=input_json, metadata=metadata, logger_context=logger_context
+        ):
+            current_file_size = os.path.getsize(current_part_path)
+            if current_file_size > file_size_limit:
+                # Upload completed part file
+                _upload_file_to_json_dataset(
+                    file_path=current_part_path,
+                    s3_metadata=s3_metadata,
+                    workflow_run_properties=workflow_run_properties,
+                    delete_upon_successful_upload=delete_upon_successful_upload,
                 )
-            )
-            logger.info("Output file attributes", extra=logger_extra)
-            # Upload compressed file
-            _upload_file_to_json_dataset(
-                file_path=compressed_output_path,
-                s3_metadata=s3_metadata,
-                workflow_run_properties=workflow_run_properties,
-                delete_upon_successful_upload=delete_upon_successful_upload,
-                upload_to_compressed_s3_prefix=True,
-            )
-            uploaded_files.append(compressed_output_path)
+                uploaded_files.append(current_part_path)
+                # Update output path to next part
+                part_number += 1
+                current_part_path = get_output_path(
+                    metadata=metadata,
+                    part_number=part_number,
+                    output_dir=output_dir,
+                    touch=True,
+                )
+            # Write block data to both part file and compressed file
+            for transformed_record in transformed_block:
+                line_count += 1
+                record_with_newline = "{}\n".format(json.dumps(transformed_record))
+                f_out.write(record_with_newline)
+                f_compressed_out.write(record_with_newline)
+    # fmt: on
+    # Upload final part
+    _upload_file_to_json_dataset(
+        file_path=current_part_path,
+        s3_metadata=s3_metadata,
+        workflow_run_properties=workflow_run_properties,
+        delete_upon_successful_upload=delete_upon_successful_upload,
+    )
+    uploaded_files.append(current_part_path)
+    logger_extra = dict(
+        merge_dicts(
+            logger_context,
+            {
+                "file.LineCount": line_count,
+                "event.kind": "metric",
+                "event.category": ["file"],
+                "event.type": ["info", "creation"],
+                "event.action": "list-file-properties",
+                "labels": {
+                    k: v.isoformat() if isinstance(v, datetime.datetime) else v
+                    for k, v in metadata.items()
+                },
+            },
+        )
+    )
+    logger.info("Output file attributes", extra=logger_extra)
+    # Upload compressed file
+    _upload_file_to_json_dataset(
+        file_path=compressed_output_path,
+        s3_metadata=s3_metadata,
+        workflow_run_properties=workflow_run_properties,
+        delete_upon_successful_upload=delete_upon_successful_upload,
+        upload_to_compressed_s3_prefix=True,
+    )
+    uploaded_files.append(compressed_output_path)
     return uploaded_files