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import json
import re
from typing import Type, TypeVar
from langchain_core.exceptions import OutputParserException
from langchain_core.output_parsers import BaseOutputParser
from langchain_core.pydantic_v1 import BaseModel, ValidationError
from langchain.output_parsers.format_instructions import PYDANTIC_FORMAT_INSTRUCTIONS
T = TypeVar("T", bound=BaseModel)
class PydanticOutputParser(BaseOutputParser[T]):
"""Parse an output using a pydantic model."""
pydantic_object: Type[T]
"""The pydantic model to parse."""
def parse(self, text: str) -> T:
try:
# Greedy search for 1st json candidate.
match = re.search(
r"\{.*\}", text.strip(), re.MULTILINE | re.IGNORECASE | re.DOTALL
)
json_str = ""
if match:
json_str = match.group()
json_object = json.loads(json_str, strict=False)
return self.pydantic_object.parse_obj(json_object)
except (json.JSONDecodeError, ValidationError) as e:
name = self.pydantic_object.__name__
msg = f"Failed to parse {name} from completion {text}. Got: {e}"
raise OutputParserException(msg, llm_output=text)
def get_format_instructions(self) -> str:
schema = self.pydantic_object.schema()
# Remove extraneous fields.
reduced_schema = schema
if "title" in reduced_schema:
del reduced_schema["title"]
if "type" in reduced_schema:
del reduced_schema["type"]
# Ensure json in context is well-formed with double quotes.
schema_str = json.dumps(reduced_schema)
return PYDANTIC_FORMAT_INSTRUCTIONS.format(schema=schema_str)
@property
def _type(self) -> str:
return "pydantic"
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