added callback for streaming response

callbacks.py

@@ -0,0 +1,17 @@
+from queue import SimpleQueue
+from langchain.callbacks.base import BaseCallbackHandler
+
+job_done = object() # signals the processing is done
+
+# https://gist.github.com/mortymike/70711b028311681e5f3c6511031d5d43
+class StreamingGradioCallbackHandler(BaseCallbackHandler):
+    """Callback handler for streaming. Only works with LLMs that support streaming."""
+
+    def __init__(self, q: SimpleQueue):
+        self.q = q
+
+    def on_llm_new_token(self, token: str, **kwargs) -> None:
+        self.q.put(token)
+
+    def on_llm_end(self, *args, **kwargs) -> None:
+        self.q.put(job_done)