core[patch]: support load from path for default namespaces (#26675)

libs/core/langchain_core/load/load.py

@@ -19,6 +19,17 @@ DEFAULT_NAMESPACES = [
     "langchain_anthropic",
     "langchain_groq",
     "langchain_google_genai",
+    "langchain_aws",
+    "langchain_openai",
+    "langchain_google_vertexai",
+    "langchain_mistralai",
+    "langchain_fireworks",
+]
+# Namespaces for which only deserializing via the SERIALIZABLE_MAPPING is allowed.
+# Load by path is not allowed.
+DISALLOW_LOAD_FROM_PATH = [
+    "langchain_community",
+    "langchain",
 ]
 
 ALL_SERIALIZABLE_MAPPINGS = {
@@ -103,39 +114,30 @@ class Reviver:
             and value.get("id", None) is not None
         ):
             [*namespace, name] = value["id"]
+            mapping_key = tuple(value["id"])
 
             if namespace[0] not in self.valid_namespaces:
                 raise ValueError(f"Invalid namespace: {value}")
-
+            # The root namespace ["langchain"] is not a valid identifier.
-            # The root namespace "langchain" is not a valid identifier.
+            elif namespace == ["langchain"]:
-            if len(namespace) == 1 and namespace[0] == "langchain":
                 raise ValueError(f"Invalid namespace: {value}")
-
+            # Has explicit import path.
-            # If namespace is in known namespaces, try to use mapping
+            elif mapping_key in self.import_mappings:
-            key = tuple(namespace + [name])
+                import_path = self.import_mappings[mapping_key]
-            if namespace[0] in DEFAULT_NAMESPACES:
+                # Split into module and name
-                # Get the importable path
+                import_dir, name = import_path[:-1], import_path[-1]
-                if key not in self.import_mappings:
+                # Import module
+                mod = importlib.import_module(".".join(import_dir))
+            elif namespace[0] in DISALLOW_LOAD_FROM_PATH:
                 raise ValueError(
                     "Trying to deserialize something that cannot "
                     "be deserialized in current version of langchain-core: "
-                        f"{key}"
+                    f"{mapping_key}."
                 )
-                import_path = self.import_mappings[key]
+            # Otherwise, treat namespace as path.
-                # Split into module and name
-                import_dir, import_obj = import_path[:-1], import_path[-1]
-                # Import module
-                mod = importlib.import_module(".".join(import_dir))
-                # Import class
-                cls = getattr(mod, import_obj)
-            # Otherwise, load by path
-            else:
-                if key in self.additional_import_mappings:
-                    import_path = self.import_mappings[key]
-                    mod = importlib.import_module(".".join(import_path[:-1]))
-                    name = import_path[-1]
             else:
                 mod = importlib.import_module(".".join(namespace))
+
             cls = getattr(mod, name)
 
             # The class must be a subclass of Serializable.