Harrison/verbose prompt (#159)

Add printing of prompt to LLMChain

docs/examples/demos/simple_prompts.ipynb

@@ -12,17 +12,32 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 1,
    "id": "51a54c4d",
    "metadata": {},
    "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "\n",
+      "\n",
+      "\u001b[1m> Entering new chain...\u001b[0m\n",
+      "Prompt after formatting:\n",
+      "\u001b[32;1m\u001b[1;3mQuestion: What NFL team won the Super Bowl in the year Justin Beiber was born?\n",
+      "\n",
+      "Answer: Let's think step by step.\u001b[0m\n",
+      "\n",
+      "\u001b[1m> Finished chain.\u001b[0m\n"
+     ]
+    },
     {
      "data": {
       "text/plain": [
        "' The year Justin Beiber was born was 1994. In 1994, the Dallas Cowboys won the Super Bowl.'"
       ]
      },
-     "execution_count": 2,
+     "execution_count": 1,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -34,7 +49,7 @@
     "\n",
     "Answer: Let's think step by step.\"\"\"\n",
     "prompt = PromptTemplate(template=template, input_variables=[\"question\"])\n",
-    "llm_chain = LLMChain(prompt=prompt, llm=OpenAI(temperature=0))\n",
+    "llm_chain = LLMChain(prompt=prompt, llm=OpenAI(temperature=0), verbose=True)\n",
     "\n",
     "question = \"What NFL team won the Super Bowl in the year Justin Beiber was born?\"\n",
     "\n",

langchain/chains/llm.py

@@ -4,6 +4,7 @@ from typing import Any, Dict, List
 from pydantic import BaseModel, Extra
 
 from langchain.chains.base import Chain
+from langchain.input import print_text
 from langchain.llms.base import LLM
 from langchain.prompts.base import BasePromptTemplate
 
@@ -53,7 +54,9 @@ class LLMChain(Chain, BaseModel):
     def _call(self, inputs: Dict[str, Any]) -> Dict[str, str]:
         selected_inputs = {k: inputs[k] for k in self.prompt.input_variables}
         prompt = self.prompt.format(**selected_inputs)
-
+        if self.verbose:
+            print("Prompt after formatting:")
+            print_text(prompt, color="green", end="\n")
         kwargs = {}
         if "stop" in inputs:
             kwargs["stop"] = inputs["stop"]