Fix sentence transformers reranker import (#231)

Sentence transformers was not being dynamically imported into the
reranker module for hugging face, causing dependency issues for anyone
using a reranker. Fixes
#229

redisvl/utils/rerank/cohere.py

@@ -83,7 +83,7 @@ def _initialize_clients(self, api_config: Optional[Dict]):
             from cohere import AsyncClient, Client
         except ImportError:
             raise ImportError(
-                "Cohere vectorizer requires the cohere library. \
+                "Cohere reranker requires the cohere library. \
                     Please install with `pip install cohere`"
             )
 

redisvl/utils/rerank/hf_cross_encoder.py

@@ -1,6 +1,6 @@
 from typing import Any, Dict, List, Optional, Tuple, Union
 
-from sentence_transformers import CrossEncoder
+from pydantic.v1 import PrivateAttr
 
 from redisvl.utils.rerank.base import BaseReranker
 
@@ -31,25 +31,44 @@ class HFCrossEncoderReranker(BaseReranker):
         )
     """
 
+    _client: Any = PrivateAttr()
+
     def __init__(
         self,
-        model_name: str = "cross-encoder/ms-marco-MiniLM-L-6-v2",
+        model: str = "cross-encoder/ms-marco-MiniLM-L-6-v2",
         limit: int = 3,
         return_score: bool = True,
+        **kwargs,
     ) -> None:
         """
         Initialize the HFCrossEncoderReranker with a specified model and ranking criteria.
 
         Parameters:
-            model_name (str): The name or path of the cross-encoder model to use for reranking.
+            model (str): The name or path of the cross-encoder model to use for reranking.
                 Defaults to 'cross-encoder/ms-marco-MiniLM-L-6-v2'.
             limit (int): The maximum number of results to return after reranking. Must be a positive integer.
             return_score (bool): Whether to return scores alongside the reranked results.
         """
+        model = model or kwargs.pop("model_name", None)
         super().__init__(
-            model=model_name, rank_by=None, limit=limit, return_score=return_score
+            model=model, rank_by=None, limit=limit, return_score=return_score
         )
-        self.model: CrossEncoder = CrossEncoder(model_name)
+        self._initialize_client(**kwargs)
+
+    def _initialize_client(self, **kwargs):
+        """
+        Setup the huggingface cross-encoder client using optional kwargs.
+        """
+        # Dynamic import of the sentence-transformers module
+        try:
+            from sentence_transformers import CrossEncoder
+        except ImportError:
+            raise ImportError(
+                "HFCrossEncoder reranker requires the sentence-transformers library. \
+                    Please install with `pip install sentence-transformers`"
+            )
+
+        self._client = CrossEncoder(self.model, **kwargs)
 
     def rank(
         self, query: str, docs: Union[List[Dict[str, Any]], List[str]], **kwargs
@@ -97,7 +116,7 @@ def rank(
             texts = [str(doc) for doc in docs]
             doc_subset = [{"content": doc} for doc in docs]
 
-        scores = self.model.predict([(query, text) for text in texts])
+        scores = self._client.predict([(query, text) for text in texts])
         scores = [float(score) for score in scores]
         docs_with_scores = list(zip(doc_subset, scores))
         docs_with_scores.sort(key=lambda x: x[1], reverse=True)