add enum output parser (langchain-ai#5165)

docs/modules/prompts/output_parsers/examples/enum.ipynb

@@ -0,0 +1,173 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "0360be02",
+   "metadata": {},
+   "source": [
+    "# Enum Output Parser\n",
+    "\n",
+    "This notebook shows how to use an Enum output parser"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "2f039b4b",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.output_parsers.enum import EnumOutputParser"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "9a35d1a7",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from enum import Enum\n",
+    "\n",
+    "class Colors(Enum):\n",
+    "    RED = \"red\"\n",
+    "    GREEN = \"green\"\n",
+    "    BLUE = \"blue\""
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "a90a66f5",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "parser = EnumOutputParser(enum=Colors)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "c48b88cb",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "<Colors.RED: 'red'>"
+      ]
+     },
+     "execution_count": 5,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "parser.parse(\"red\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "7d313e41",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "<Colors.GREEN: 'green'>"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# Can handle spaces\n",
+    "parser.parse(\" green\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "976ae42d",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "<Colors.BLUE: 'blue'>"
+      ]
+     },
+     "execution_count": 7,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "# And new lines\n",
+    "parser.parse(\"blue\\n\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "636a48ab",
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "OutputParserException",
+     "evalue": "Response 'yellow' is not one of the expected values: ['red', 'green', 'blue']",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
+      "File \u001b[0;32m~/workplace/langchain/langchain/output_parsers/enum.py:25\u001b[0m, in \u001b[0;36mEnumOutputParser.parse\u001b[0;34m(self, response)\u001b[0m\n\u001b[1;32m     24\u001b[0m \u001b[38;5;28;01mtry\u001b[39;00m:\n\u001b[0;32m---> 25\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[38;5;28;43mself\u001b[39;49m\u001b[38;5;241;43m.\u001b[39;49m\u001b[43menum\u001b[49m\u001b[43m(\u001b[49m\u001b[43mresponse\u001b[49m\u001b[38;5;241;43m.\u001b[39;49m\u001b[43mstrip\u001b[49m\u001b[43m(\u001b[49m\u001b[43m)\u001b[49m\u001b[43m)\u001b[49m\n\u001b[1;32m     26\u001b[0m \u001b[38;5;28;01mexcept\u001b[39;00m \u001b[38;5;167;01mValueError\u001b[39;00m:\n",
+      "File \u001b[0;32m~/.pyenv/versions/3.9.1/lib/python3.9/enum.py:315\u001b[0m, in \u001b[0;36mEnumMeta.__call__\u001b[0;34m(cls, value, names, module, qualname, type, start)\u001b[0m\n\u001b[1;32m    314\u001b[0m \u001b[38;5;28;01mif\u001b[39;00m names \u001b[38;5;129;01mis\u001b[39;00m \u001b[38;5;28;01mNone\u001b[39;00m:  \u001b[38;5;66;03m# simple value lookup\u001b[39;00m\n\u001b[0;32m--> 315\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[38;5;28;43mcls\u001b[39;49m\u001b[38;5;241;43m.\u001b[39;49m\u001b[38;5;21;43m__new__\u001b[39;49m\u001b[43m(\u001b[49m\u001b[38;5;28;43mcls\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[43mvalue\u001b[49m\u001b[43m)\u001b[49m\n\u001b[1;32m    316\u001b[0m \u001b[38;5;66;03m# otherwise, functional API: we're creating a new Enum type\u001b[39;00m\n",
+      "File \u001b[0;32m~/.pyenv/versions/3.9.1/lib/python3.9/enum.py:611\u001b[0m, in \u001b[0;36mEnum.__new__\u001b[0;34m(cls, value)\u001b[0m\n\u001b[1;32m    610\u001b[0m \u001b[38;5;28;01mif\u001b[39;00m result \u001b[38;5;129;01mis\u001b[39;00m \u001b[38;5;28;01mNone\u001b[39;00m \u001b[38;5;129;01mand\u001b[39;00m exc \u001b[38;5;129;01mis\u001b[39;00m \u001b[38;5;28;01mNone\u001b[39;00m:\n\u001b[0;32m--> 611\u001b[0m     \u001b[38;5;28;01mraise\u001b[39;00m ve_exc\n\u001b[1;32m    612\u001b[0m \u001b[38;5;28;01melif\u001b[39;00m exc \u001b[38;5;129;01mis\u001b[39;00m \u001b[38;5;28;01mNone\u001b[39;00m:\n",
+      "\u001b[0;31mValueError\u001b[0m: 'yellow' is not a valid Colors",
+      "\nDuring handling of the above exception, another exception occurred:\n",
+      "\u001b[0;31mOutputParserException\u001b[0m                     Traceback (most recent call last)",
+      "Cell \u001b[0;32mIn[8], line 2\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[38;5;66;03m# And raises errors when appropriate\u001b[39;00m\n\u001b[0;32m----> 2\u001b[0m \u001b[43mparser\u001b[49m\u001b[38;5;241;43m.\u001b[39;49m\u001b[43mparse\u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;124;43m\"\u001b[39;49m\u001b[38;5;124;43myellow\u001b[39;49m\u001b[38;5;124;43m\"\u001b[39;49m\u001b[43m)\u001b[49m\n",
+      "File \u001b[0;32m~/workplace/langchain/langchain/output_parsers/enum.py:27\u001b[0m, in \u001b[0;36mEnumOutputParser.parse\u001b[0;34m(self, response)\u001b[0m\n\u001b[1;32m     25\u001b[0m     \u001b[38;5;28;01mreturn\u001b[39;00m \u001b[38;5;28mself\u001b[39m\u001b[38;5;241m.\u001b[39menum(response\u001b[38;5;241m.\u001b[39mstrip())\n\u001b[1;32m     26\u001b[0m \u001b[38;5;28;01mexcept\u001b[39;00m \u001b[38;5;167;01mValueError\u001b[39;00m:\n\u001b[0;32m---> 27\u001b[0m     \u001b[38;5;28;01mraise\u001b[39;00m OutputParserException(\n\u001b[1;32m     28\u001b[0m         \u001b[38;5;124mf\u001b[39m\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mResponse \u001b[39m\u001b[38;5;124m'\u001b[39m\u001b[38;5;132;01m{\u001b[39;00mresponse\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m'\u001b[39m\u001b[38;5;124m is not one of the \u001b[39m\u001b[38;5;124m\"\u001b[39m\n\u001b[1;32m     29\u001b[0m         \u001b[38;5;124mf\u001b[39m\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mexpected values: \u001b[39m\u001b[38;5;132;01m{\u001b[39;00m\u001b[38;5;28mself\u001b[39m\u001b[38;5;241m.\u001b[39m_valid_values\u001b[38;5;132;01m}\u001b[39;00m\u001b[38;5;124m\"\u001b[39m\n\u001b[1;32m     30\u001b[0m     )\n",
+      "\u001b[0;31mOutputParserException\u001b[0m: Response 'yellow' is not one of the expected values: ['red', 'green', 'blue']"
+     ]
+    }
+   ],
+   "source": [
+    "# And raises errors when appropriate\n",
+    "parser.parse(\"yellow\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "c517f447",
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.9.1"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

langchain/output_parsers/enum.py

@@ -0,0 +1,33 @@
+from enum import Enum
+from typing import Any, Dict, List, Type
+
+from pydantic import root_validator
+
+from langchain.schema import BaseOutputParser, OutputParserException
+
+
+class EnumOutputParser(BaseOutputParser):
+    enum: Type[Enum]
+
+    @root_validator()
+    def raise_deprecation(cls, values: Dict) -> Dict:
+        enum = values["enum"]
+        if not all(isinstance(e.value, str) for e in enum):
+            raise ValueError("Enum values must be strings")
+        return values
+
+    @property
+    def _valid_values(self) -> List[str]:
+        return [e.value for e in self.enum]
+
+    def parse(self, response: str) -> Any:
+        try:
+            return self.enum(response.strip())
+        except ValueError:
+            raise OutputParserException(
+                f"Response '{response}' is not one of the "
+                f"expected values: {self._valid_values}"
+            )
+
+    def get_format_instructions(self) -> str:
+        return f"Select one of the following options: {', '.join(self._valid_values)}"

tests/unit_tests/output_parsers/test_enum_parser.py

@@ -0,0 +1,31 @@
+from enum import Enum
+
+from langchain.output_parsers.enum import EnumOutputParser
+from langchain.schema import OutputParserException
+
+
+class Colors(Enum):
+    RED = "red"
+    GREEN = "green"
+    BLUE = "blue"
+
+
+def test_enum_output_parser_parse() -> None:
+    parser = EnumOutputParser(enum=Colors)
+
+    # Test valid inputs
+    result = parser.parse("red")
+    assert result == Colors.RED
+
+    result = parser.parse("green")
+    assert result == Colors.GREEN
+
+    result = parser.parse("blue")
+    assert result == Colors.BLUE
+
+    # Test invalid input
+    try:
+        parser.parse("INVALID")
+        assert False, "Should have raised OutputParserException"
+    except OutputParserException:
+        pass