from langchain_core.output_parsers import JsonOutputParser
from langchain_core.prompts import PromptTemplate
from langchain_core.pydantic_v1 import BaseModel, Field
from langchain_openai import ChatOpenAI

model = ChatOpenAI(temperature=0)

class Person(BaseModel):
    name: str = Field(description="The name of the person")
    lastname: str = Field(description="The lastname of the person")

prompt = PromptTemplate(
    template="Extract information about a person.\n{format_instructions}\n{query}\n",
    input_variables=["query"],
    partial_variables={"format_instructions": parser.get_format_instructions()},
)

chain = prompt | model | JsonOutputParser(pydantic_object=Person)

chain.invoke({"query": "There is a person called John Doe that lives in the city."})