refactor(ingest/s3): enhance readability

- Refactor S3Source().get_folder_info() to enhance readability
- Add a test to ensure that get_folder_info() returns the expected result.

Author: eagle-25

metadata-ingestion/src/datahub/ingestion/source/s3/source.py

@@ -847,7 +847,7 @@ def get_folder_info(
         path_spec: PathSpec,
         bucket: "Bucket",
         prefix: str,
-    ) -> List[Folder]:
+    ) -> Iterable[Folder]:
         """
         Retrieves all the folders in a path by listing all the files in the prefix.
         If the prefix is a full path then only that folder will be extracted.
@@ -877,51 +877,30 @@ def _is_allowed_path(path_spec_: PathSpec, s3_uri: str) -> bool:
         s3_objects = (
             obj
             for obj in bucket.objects.filter(Prefix=prefix).page_size(PAGE_SIZE)
-            if _is_allowed_path(path_spec, f"s3://{obj.bucket_name}/{obj.key}")
+            if _is_allowed_path(
+                path_spec, self.create_s3_path(obj.bucket_name, obj.key)
+            )
         )
-
-        partitions: List[Folder] = []
         grouped_s3_objects_by_dirname = groupby_unsorted(
             s3_objects,
             key=lambda obj: obj.key.rsplit("/", 1)[0],
         )
-        for key, group in grouped_s3_objects_by_dirname:
-            file_size = 0
-            creation_time = None
-            modification_time = None
-
-            for item in group:
-                file_size += item.size
-                if creation_time is None or item.last_modified < creation_time:
-                    creation_time = item.last_modified
-                if modification_time is None or item.last_modified > modification_time:
-                    modification_time = item.last_modified
-                    max_file = item
-
-            if modification_time is None:
-                logger.warning(
-                    f"Unable to find any files in the folder {key}. Skipping..."
-                )
-                continue
-
-            id = path_spec.get_partition_from_path(
-                self.create_s3_path(max_file.bucket_name, max_file.key)
+        for _, group in grouped_s3_objects_by_dirname:
+            max_file = max(group, key=lambda x: x.last_modified)
+            max_file_s3_path = self.create_s3_path(max_file.bucket_name, max_file.key)
+
+            # If partition_id is None, it means the folder is not a partition
+            partition_id = path_spec.get_partition_from_path(max_file_s3_path)
+
+            yield Folder(
+                partition_id=partition_id,
+                is_partition=bool(partition_id),
+                creation_time=min(obj.last_modified for obj in group),
+                modification_time=max_file.last_modified,
+                sample_file=max_file_s3_path,
+                size=sum(obj.size for obj in group),
             )
 
-            # If id is None, it means the folder is not a partition
-            partitions.append(
-                Folder(
-                    partition_id=id,
-                    is_partition=bool(id),
-                    creation_time=creation_time if creation_time else None,  # type: ignore[arg-type]
-                    modification_time=modification_time,
-                    sample_file=self.create_s3_path(max_file.bucket_name, max_file.key),
-                    size=file_size,
-                )
-            )
-
-        return partitions
-
     def s3_browser(self, path_spec: PathSpec, sample_size: int) -> Iterable[BrowsePath]:
         if self.source_config.aws_config is None:
             raise ValueError("aws_config not set. Cannot browse s3")
@@ -1000,7 +979,7 @@ def s3_browser(self, path_spec: PathSpec, sample_size: int) -> Iterable[BrowsePa
                                     min=True,
                                 )
                                 dirs_to_process.append(dirs_to_process_min[0])
-                        folders = []
+                        folders: List[Folder] = []
                         for dir in dirs_to_process:
                             logger.info(f"Getting files from folder: {dir}")
                             prefix_to_process = urlparse(dir).path.lstrip("/")

metadata-ingestion/tests/unit/s3/test_s3_source.py

@@ -9,7 +9,11 @@
 from datahub.ingestion.api.workunit import MetadataWorkUnit
 from datahub.ingestion.source.data_lake_common.data_lake_utils import ContainerWUCreator
 from datahub.ingestion.source.data_lake_common.path_spec import PathSpec
-from datahub.ingestion.source.s3.source import S3Source, partitioned_folder_comparator
+from datahub.ingestion.source.s3.source import (
+    Folder,
+    S3Source,
+    partitioned_folder_comparator,
+)
 
 
 def _get_s3_source(path_spec_: PathSpec) -> S3Source:
@@ -257,7 +261,7 @@ def container_properties_filter(x: MetadataWorkUnit) -> bool:
     }
 
 
-def test_get_folder_info():
+def test_get_folder_info_returns_latest_file_in_each_folder() -> None:
     """
     Test S3Source.get_folder_info returns the latest file in each folder
     """
@@ -298,6 +302,7 @@ def test_get_folder_info():
     res = _get_s3_source(path_spec).get_folder_info(
         path_spec, bucket, prefix="/my-folder"
     )
+    res = list(res)
 
     # assert
     assert len(res) == 2
@@ -336,6 +341,7 @@ def test_get_folder_info_ignores_disallowed_path(
 
     # act
     res = s3_source.get_folder_info(path_spec, bucket, prefix="/my-folder")
+    res = list(res)
 
     # assert
     expected_called_s3_uri = "s3://my-bucket/my-folder/ignore/this/path/0001.csv"
@@ -350,3 +356,48 @@ def test_get_folder_info_ignores_disallowed_path(
         "Dropped file should be in the report.filtered"
     )
     assert res == [], "Dropped file should not be in the result"
+
+
+def test_get_folder_info_returns_expected_folder() -> None:
+    # arrange
+    path_spec = PathSpec(
+        include="s3://my-bucket/{table}/{partition0}/*.csv",
+        table_name="{table}",
+    )
+
+    bucket = Mock()
+    bucket.objects.filter().page_size = Mock(
+        return_value=[
+            Mock(
+                bucket_name="my-bucket",
+                key="my-folder/dir1/0001.csv",
+                creation_time=datetime(2025, 1, 1, 1),
+                last_modified=datetime(2025, 1, 1, 1),
+                size=100,
+            ),
+            Mock(
+                bucket_name="my-bucket",
+                key="my-folder/dir1/0002.csv",
+                creation_time=datetime(2025, 1, 1, 2),
+                last_modified=datetime(2025, 1, 1, 2),
+                size=50,
+            ),
+        ]
+    )
+
+    # act
+    res = _get_s3_source(path_spec).get_folder_info(
+        path_spec, bucket, prefix="/my-folder"
+    )
+    res = list(res)
+
+    # assert
+    assert len(res) == 1
+    assert res[0] == Folder(
+        partition_id=[("partition0", "dir1")],
+        is_partition=True,
+        creation_time=datetime(2025, 1, 1, 1),
+        modification_time=datetime(2025, 1, 1, 2),
+        size=150,
+        sample_file="s3://my-bucket/my-folder/dir1/0002.csv",
+    )