Pydantic Models in Python
From the FastAPI cheat sheet · Request Body & Pydantic Models · verified Jul 2026
Pydantic Models
Define request and response schemas with automatic validation.
python
from pydantic import BaseModel, Field
class Item(BaseModel):
name: str
price: float = Field(gt=0, description="Must be positive")
description: str | None = None
tags: list[str] = []
@app.post("/items/")
async def create_item(item: Item):
return item💡 Pydantic model parameters are automatically parsed from the JSON request body
⚡ Use Field() for validation: gt, ge, lt, le (numbers), min_length, max_length (strings)
📌 Nested models are fully validated — define Address as a model and use it inside User
🟢 FastAPI auto-detects: path params from URL, body from Pydantic models, rest as query
pydanticmodelsbodyvalidation
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