Custom validation with validator decorator in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the validator decorator from pydantic.

FastAPI

from pydantic import BaseModel, [1]

Drag options to blanks, or click blank then click option'

Avalidate_field

Bvalidate

Ccheck

Dvalidator

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'validate' instead of 'validator' causes import errors.

Trying to import a non-existent decorator like 'check'.

The validator decorator is imported from pydantic to create custom validation methods.

2fill in blank

medium

Complete the method decorator to validate the 'name' field.

FastAPI

class User(BaseModel):
    name: str

    @[1]('name')
    def name_must_be_capitalized(cls, v):
        if not v.istitle():
            raise ValueError('Name must be capitalized')
        return v

Drag options to blanks, or click blank then click option'

Avalidate

Bvalidator

Ccheck

Dvalidate_field

Attempts:

3 left

💡 Hint

Common Mistakes

Using '@validate' instead of '@validator' causes runtime errors.

Forgetting to specify the field name in the decorator.

The @validator('name') decorator marks the method as a validator for the 'name' field.

3fill in blank

hard

Fix the error in the validator method to correctly raise an exception when validation fails.

FastAPI

from pydantic import BaseModel, validator

class Product(BaseModel):
    price: float

    @validator('price')
    def price_must_be_positive(cls, v):
        if v <= 0:
            raise [1]('Price must be positive')
        return v

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AException

BRuntimeError

CValueError

DTypeError

Attempts:

3 left

💡 Hint

Common Mistakes

Raising generic Exception does not provide clear validation error.

Using TypeError is incorrect because the type is correct but the value is invalid.

Raising ValueError is the correct way to signal validation errors in Pydantic validators.

4fill in blank

hard

Fill both blanks to create a validator that checks the 'email' field is lowercase and contains '@'.

FastAPI

class Contact(BaseModel):
    email: str

    @[1]('email')
    def email_must_be_valid(cls, v):
        if '@' not in v or v != v.[2]():
            raise ValueError('Email must be lowercase and contain @')
        return v

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Avalidator

Bvalidate

Clower

Dupper

Attempts:

3 left

💡 Hint

Common Mistakes

Using '@validate' instead of '@validator' causes errors.

Using 'upper' instead of 'lower' reverses the logic.

The @validator('email') decorator marks the method for the 'email' field. Using v.lower() checks if the email is lowercase.

5fill in blank

hard

Fill all three blanks to create a validator that ensures 'age' is an integer and at least 18.

FastAPI

class Person(BaseModel):
    age: int

    @[1]('age')
    def age_must_be_adult(cls, v):
        if not isinstance(v, [2]) or v < [3]:
            raise ValueError('Age must be an integer and at least 18')
        return v

Drag options to blanks, or click blank then click option'

Avalidator

Bint

C18

Dfloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'float' instead of 'int' in isinstance check.

Using a wrong minimum age value.

The @validator('age') decorator marks the method for the 'age' field. isinstance(v, int) checks the type, and 18 is the minimum age.