fix: raise a ValueError for a glossary CSV row without a target

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: hive-bot

CHANGELOG.md

@@ -249,6 +249,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   the `glossary` parameter. Calling it emits a `DeprecationWarning`.
 
 ### Fixed
+- A glossary CSV row without a target term now raises a `ValueError` naming
+  the row; previously a bare `IndexError` (it is still an `IndexError`).
 - A connection that is reset or breaks off while the response body is read
   is now retried like other connection failures, and raises
   `ConnectionException` with `should_retry` `True` once retries are used up.

deepl/util.py

@@ -183,6 +183,11 @@ def convert_dict_to_tsv(
     )
 
 
+class _GlossaryCsvRowError(ValueError, IndexError):
+    """ValueError for an invalid CSV row; also an IndexError, which earlier
+    versions raised."""
+
+
 def convert_csv_to_dict(
     csv_data: Union[TextIO, BinaryIO, str, bytes, Any],
     skip_checks: bool = False,
@@ -216,6 +221,8 @@ def convert_csv_to_dict(
     for line, index in zip(reader, itertools.count(1)):
         if not line:
             continue
+        if len(line) < 2:
+            raise _GlossaryCsvRowError(f"Entry {index} has no target term")
         source, target = line[0].strip(), line[1].strip()
         if source in entries_dict:
             raise ValueError(

tests/offline/test_util.py

@@ -38,6 +38,12 @@ def test_convert_dict_to_tsv():
         deepl.convert_dict_to_tsv({"\t": "target"})
 
 
+def test_glossary_csv_row_without_target_raises_value_error():
+    with pytest.raises(ValueError, match="Entry 1 has no target term") as e:
+        deepl.util.convert_csv_to_dict("hello\n")
+    assert isinstance(e.value, IndexError)
+
+
 def test_parse_timestamp_microseconds():
     """Standard 6-digit fractional seconds should parse correctly."""
     result = parse_timestamp("2025-01-15T10:30:00.123456+0000")