fix(csv): warn when empty input produces empty markdown

packages/markitdown/src/markitdown/converters/_csv_converter.py

@@ -2,6 +2,7 @@
 import io
 import re
 from typing import BinaryIO, Any
+from warnings import warn
 from charset_normalizer import from_bytes
 from .._base_converter import DocumentConverter, DocumentConverterResult
 from .._stream_info import StreamInfo
@@ -105,6 +106,11 @@ def convert(
         _trim_outer_blank_rows(rows)
 
         if not rows:
+            warn(
+                "CSV input is empty or contains only blank rows; producing empty markdown.",
+                UserWarning,
+                stacklevel=2,
+            )
             return DocumentConverterResult(markdown="")
 
         # Pad all rows, including the header, to preserve the widest row.

packages/markitdown/tests/test_csv.py

@@ -6,7 +6,6 @@
 
 from markitdown import MarkItDown, StreamInfo
 
-
 # Record separators
 
 
@@ -72,10 +71,20 @@ def test_csv_long_blank_runs(position: str) -> None:
         "all": blank,
     }[position]
 
-    result = MarkItDown(enable_plugins=False).convert_stream(
-        io.BytesIO(content),
-        stream_info=StreamInfo(extension=".csv", charset="utf-8"),
-    )
+    if position == "all":
+        with pytest.warns(
+            UserWarning,
+            match="CSV input is empty or contains only blank rows",
+        ):
+            result = MarkItDown(enable_plugins=False).convert_stream(
+                io.BytesIO(content),
+                stream_info=StreamInfo(extension=".csv", charset="utf-8"),
+            )
+    else:
+        result = MarkItDown(enable_plugins=False).convert_stream(
+            io.BytesIO(content),
+            stream_info=StreamInfo(extension=".csv", charset="utf-8"),
+        )
 
     expected = (
         "| name | value |  |\n"
@@ -138,8 +147,13 @@ def test_csv_blank_lines_between_rows_are_kept() -> None:
     )
 
 
-def test_csv_all_blank_input_returns_empty_markdown() -> None:
-    result = _convert_csv(b"\n\n\n")
+@pytest.mark.parametrize("data", [b"", b"\n\n\n"])
+def test_csv_empty_input_warns_and_returns_empty_markdown(data: bytes) -> None:
+    with pytest.warns(
+        UserWarning,
+        match="CSV input is empty or contains only blank rows",
+    ):
+        result = _convert_csv(data)
 
     assert result == ""