Ensure presence of head and tail entity in the original sentence

flair/models/relation_classifier_model.py

@@ -258,7 +258,7 @@ def __init__(
         allow_unk_tag: bool = True,
         max_allowed_tokens_between_entities: int = 20,
         max_surrounding_context_length: int = 10,
-        **classifierargs,
+        **classifierargs: Any,
     ) -> None:
         """Initializes a `RelationClassifier`.
 
@@ -435,8 +435,8 @@ def _encode_sentence(
         # since there may be multiple occurrences of the same entity mentioned in the sentence.
         # Therefore, we use the span's position in the sentence.
         encoded_sentence_tokens: list[str] = []
-        head_idx = -10000
-        tail_idx = 10000
+        head_idx: Optional[int] = None
+        tail_idx: Optional[int] = None
         for token in original_sentence:
             if token is head.span[0]:
                 head_idx = len(encoded_sentence_tokens)
@@ -452,11 +452,19 @@ def _encode_sentence(
             ):
                 encoded_sentence_tokens.append(token.text)
 
-        # filter cases in which the distance between the two entities is too large
+        msg: str
+        if head_idx is None:
+            msg = f"The head entity ({head!r}) is not located inside the original sentence ({original_sentence!r})."
+            raise AssertionError(msg)
+        if tail_idx is None:
+            msg = f"The tail entity ({tail!r}) is not located inside the original sentence ({original_sentence!r})."
+            raise AssertionError(msg)
+
+        # Filter cases in which the distance between the two entities is too large
         if abs(head_idx - tail_idx) > self._max_allowed_tokens_between_entities:
             return None
 
-        # remove excess tokens left and right of entity pair to make encoded sentence shorter
+        # Remove excess tokens left and right of entity pair to make encoded sentence shorter
         encoded_sentence_tokens = self._slice_encoded_sentence_to_max_allowed_length(
             encoded_sentence_tokens, head_idx, tail_idx
         )