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Explanation

Input validation checks whether incoming API data follows the expected structure, types, and business rules.

Code:

Request JSON
   |
   v
Validation
   |
   +-- Valid → Continue
   |
   +-- Invalid → 400 Response

Explanation

Pydantic models can define the expected structure and data types for incoming data.

Code:

from pydantic import BaseModel

class UserCreate(BaseModel):
    name: str
    email: str
    age: int

Explanation

Validate incoming JSON using a Pydantic model before passing data to the service layer.

Code:

@app.post('/users')
def create_user():
    data = UserCreate(**request.get_json())
    return data.model_dump(), 201

Explanation

Marshmallow provides schemas for serialization and deserialization of Python objects and request data.

Code:

from marshmallow import Schema, fields

class UserSchema(Schema):
    name = fields.Str(required=True)
    email = fields.Email(required=True)
    age = fields.Int(required=True)

Explanation

Validation errors should be converted into clear API responses rather than allowing invalid data to reach the database.

Code:

{
  "error": "VALIDATION_ERROR",
  "fields": {
    "email": "Invalid email"
  }
}