What is structured output (JSON mode) in the Gemini API and how do you implement it?

from google import genai
from google.genai import types
from pydantic import BaseModel
from typing import Literal

client = genai.Client()

# Define schema with Pydantic
class CodeReview(BaseModel):
    summary: str
    bugs: list[str]
    severity: Literal["low", "medium", "high", "critical"]
    line_numbers: list[int]
    suggested_fix: str

# generateContent with response_schema:
response = client.models.generate_content(
    model="gemini-3.5-flash",
    contents="Review this Python code: def add(a, b): return a - b",
    config=types.GenerateContentConfig(
        response_mime_type="application/json",
        response_schema=CodeReview,
    )
)
import json
review = CodeReview(**json.loads(response.text))
print(f"Severity: {review.severity}")
print(f"Bugs: {review.bugs}")

# Interactions API structured output:
interaction = client.interactions.create(
    model="gemini-3.5-flash",
    input="Extract: Alice is 30, an engineer from London.",
    response_mime_type="application/json",
    response_schema={"type": "object",
                     "properties": {
                         "name": {"type": "string"},
                         "age": {"type": "integer"},
                         "role": {"type": "string"},
                         "city": {"type": "string"}
                     }}
)
data = json.loads(interaction.output_text)