Harrison/handle stop tokens ai21 (#1077)

Co-authored-by: Andrew Huang <jhuang16888@gmail.com>

langchain/llms/ai21.py

@@ -1,5 +1,5 @@
 """Wrapper around AI21 APIs."""
-from typing import Any, Dict, List, Mapping, Optional
+from typing import Any, Dict, List, Optional
 
 import requests
 from pydantic import BaseModel, Extra, root_validator
@@ -64,6 +64,8 @@ class AI21(LLM, BaseModel):
 
     ai21_api_key: Optional[str] = None
 
+    stop: Optional[List[str]] = None
+
     base_url: Optional[str] = None
     """Base url to use, if None decides based on model name."""
 
@@ -80,7 +82,7 @@ class AI21(LLM, BaseModel):
         return values
 
     @property
-    def _default_params(self) -> Mapping[str, Any]:
+    def _default_params(self) -> Dict[str, Any]:
         """Get the default parameters for calling AI21 API."""
         return {
             "temperature": self.temperature,
@@ -95,7 +97,7 @@ class AI21(LLM, BaseModel):
         }
 
     @property
-    def _identifying_params(self) -> Mapping[str, Any]:
+    def _identifying_params(self) -> Dict[str, Any]:
         """Get the identifying parameters."""
         return {**{"model": self.model}, **self._default_params}
 
@@ -119,7 +121,11 @@ class AI21(LLM, BaseModel):
 
                 response = ai21("Tell me a joke.")
         """
-        if stop is None:
+        if self.stop is not None and stop is not None:
+            raise ValueError("`stop` found in both the input and default params.")
+        elif self.stop is not None:
+            stop = self.stop
+        elif stop is None:
             stop = []
         if self.base_url is not None:
             base_url = self.base_url