Langchain Basics Gemini Rules

from langchain_google_genai import ChatGoogleGenerativeAI
from langchain_core.prompts import ChatPromptTemplate
from pydantic import BaseModel
from typing import List,Optional
from langchain_core.output_parsers import PydanticOutputParser


from dotenv import load_dotenv
load_dotenv()

model = ChatGoogleGenerativeAI(model="gemini-2.5-flash-lite")

class Movie(BaseModel):
    title: str
    release_year: Optional[int]
    genre: List[str]
    director: str
    cast: List[str]
    rating: float
    summary: str

parser= PydanticOutputParser(pydantic_object=Movie)

template = ChatPromptTemplate.from_messages([
    ("system",
"""
Extract movie information from the paragraph

STRICT RULES:
- Output ONLY valid JSON
- No explanations, no markdown, no extra text
- Follow the format EXACTLY

{format_instructions}
"""),
("human",
"""
{paragraph}
""")
])

para = input("give me a paragraph: ")

prompt = template.invoke(
    {
        "paragraph":para,
        "format_instructions":parser.get_format_instructions()
     }
)

response = model.invoke(prompt)
parsed_output = parser.parse(response.content)
print(parsed_output)