Harrison/backwards compat (#740)

Author: hwchase17

langchain/embeddings/__init__.py

@@ -1,12 +1,39 @@
 """Wrappers around embedding modules."""
+import logging
+from typing import Any
+
 from langchain.embeddings.cohere import CohereEmbeddings
 from langchain.embeddings.huggingface import HuggingFaceEmbeddings
 from langchain.embeddings.huggingface_hub import HuggingFaceHubEmbeddings
 from langchain.embeddings.openai import OpenAIEmbeddings
 
+logger = logging.getLogger(__name__)
+
 __all__ = [
     "OpenAIEmbeddings",
     "HuggingFaceEmbeddings",
     "CohereEmbeddings",
     "HuggingFaceHubEmbeddings",
 ]
+
+
+# TODO: this is in here to maintain backwards compatibility
+class HypotheticalDocumentEmbedder:
+    def __init__(self, *args: Any, **kwargs: Any):
+        logger.warning(
+            "Using a deprecated class. Please use "
+            "`from langchain.chains import HypotheticalDocumentEmbedder` instead"
+        )
+        from langchain.chains.hyde.base import HypotheticalDocumentEmbedder as H
+
+        return H(*args, **kwargs)  # type: ignore
+
+    @classmethod
+    def from_llm(cls, *args: Any, **kwargs: Any) -> Any:
+        logger.warning(
+            "Using a deprecated class. Please use "
+            "`from langchain.chains import HypotheticalDocumentEmbedder` instead"
+        )
+        from langchain.chains.hyde.base import HypotheticalDocumentEmbedder as H
+
+        return H.from_llm(*args, **kwargs)