fix: raise DeepLException when translate_text() gets too few translations

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

Author: hive-bot

CHANGELOG.md

@@ -138,6 +138,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed `translate_text()` raising `TypeError` when a translation in the
   response has no `billed_characters`. `TextResult.billed_characters` is now
   `None` in that case.
+- Fixed `translate_text()` raising `IndexError` when the response holds fewer
+  translations than texts sent. It now raises `DeepLException`.
 - Fixed the `DeprecationWarning` messages of `Usage.Detail.limit_exceeded` and
   `Usage.any_limit_exceeded`, which named the replacement instead of the
   deprecated property. They now read "limit_exceeded is deprecated, use

deepl/translator.py

@@ -428,6 +428,7 @@ def translate_text(
             raise TypeError(
                 "text parameter must be a string or an iterable of strings"
             )
+        text_count = len(text)
 
         request_data = self._check_language_and_formality(
             source_lang,
@@ -517,6 +518,12 @@ def join_tags(tag_argument: Union[str, Iterable[str]]) -> List[str]:
                 )
             )
 
+        if len(output) < text_count:
+            raise DeepLException(
+                f"Expected {text_count} translations in the response, "
+                f"received {len(output)}"
+            )
+
         return output if multi_input else output[0]
 
     def translate_text_with_glossary(

tests/offline/test_translate_text.py

@@ -28,6 +28,7 @@ def reply_with_translation(mocked, body):
                     "billed_characters": 5,
                 }
             ]
+            * len(body["text"])
         },
         match=json_request(body),
     )
@@ -367,6 +368,21 @@ def test_parses_tag_handling_version(mocked, translation, expected):
     assert result.tag_handling_version == expected
 
 
+@pytest.mark.parametrize(
+    "text, response",
+    [
+        ("hello", {"translations": []}),
+        ("hello", {}),
+        (["x", "y"], {"translations": [{"text": "a"}]}),
+    ],
+)
+def test_raises_when_response_has_too_few_translations(mocked, text, response):
+    mocked.post(url("v2/translate"), json=response)
+
+    with pytest.raises(deepl.DeepLException, match="translations"):
+        make_translator().translate_text(text, target_lang="DE")
+
+
 def test_parses_text_list_into_list_of_results(mocked):
     mocked.post(
         url("v2/translate"),