regex output parser (#435)

langchain/evaluation/qa/generate_prompt.py

@@ -1,24 +1,6 @@
 # flake8: noqa
-import re
-from typing import Dict
-
 from langchain.prompts import PromptTemplate
-from langchain.prompts.base import BaseOutputParser
+from langchain.prompts.base import RegexParser
-
-
-class QAGenerationOutputParser(BaseOutputParser):
-    """Parse output in question/answer pair."""
-
-    def parse(self, text: str) -> Dict[str, str]:
-        regex = r"QUESTION: (.*?)\nANSWER: (.*)"
-        match = re.search(regex, text)
-        if match:
-            question = match.group(1)
-            answer = match.group(2)
-            return {"query": question, "answer": answer}
-        else:
-            raise ValueError(f"Could not parse output: {text}")
-
 
 template = """You are a teacher coming up with questions to ask on a quiz. 
 Given the following document, please generate a question and answer based on that document.
@@ -35,6 +17,9 @@ These questions should be detailed and be based explicitly on information in the
 <Begin Document>
 {doc}
 <End Document>"""
-PROMPT = PromptTemplate(
+output_parser = RegexParser(
-    input_variables=["doc"], template=template, output_parser=QAGenerationOutputParser()
+    regex=r"QUESTION: (.*?)\nANSWER: (.*)", output_keys=["question", "answer"]
+)
+PROMPT = PromptTemplate(
+    input_variables=["doc"], template=template, output_parser=output_parser
 )

langchain/prompts/base.py

@@ -1,5 +1,6 @@
 """BasePrompt schema definition."""
 import json
+import re
 from abc import ABC, abstractmethod
 from pathlib import Path
 from typing import Any, Callable, Dict, List, Optional, Union
@@ -55,7 +56,7 @@ class BaseOutputParser(ABC):
         """Parse the output of an LLM call."""
 
 
-class ListOutputParser(ABC):
+class ListOutputParser(BaseOutputParser):
     """Class to parse the output of an LLM call to a list."""
 
     @abstractmethod
@@ -63,6 +64,21 @@ class ListOutputParser(ABC):
         """Parse the output of an LLM call."""
 
 
+class RegexParser(BaseOutputParser, BaseModel):
+    """Class to parse the output into a dictionary."""
+
+    regex: str
+    output_keys: List[str]
+
+    def parse(self, text: str) -> Dict[str, str]:
+        """Parse the output of an LLM call."""
+        match = re.search(self.regex, text)
+        if match:
+            return {key: match.group(i) for i, key in enumerate(self.output_keys)}
+        else:
+            raise ValueError(f"Could not parse output: {text}")
+
+
 class BasePromptTemplate(BaseModel, ABC):
     """Base prompt should expose the format method, returning a prompt."""