List and set validation in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main difference between a list and a set in Python?

A list keeps the order of items and allows duplicates, while a set does not keep order and automatically removes duplicates.

beginner

How do you declare a list of integers in a FastAPI request body using Pydantic?

Use List[int] from typing in the Pydantic model to specify a list of integers.

intermediate

How can you validate a set of strings in FastAPI using Pydantic?

Use Set[str] from typing in the Pydantic model. FastAPI will ensure the input is a set with unique strings.

intermediate

Why might you choose a set over a list for input validation in FastAPI?

Because sets automatically remove duplicates, they are useful when you want to ensure all items are unique without extra code.

intermediate

What happens if you send duplicate items in a list validated as a set in FastAPI?

FastAPI will convert the input to a set, removing duplicates before passing it to your endpoint logic.

In FastAPI, which type hint ensures the input is a list of strings?

A Set[str]

B List[str]

C Dict[str, str]

D Tuple[str]

List[str] tells FastAPI to expect a list of strings, preserving order and duplicates.

Which Python type automatically removes duplicate items?

A List

B Dict

C Set

D Tuple

Sets do not allow duplicates and automatically remove them.

How do you import the type hint for a set in FastAPI models?

A from typing import Set

B from fastapi import Set

C from pydantic import Set

D from collections import Set

Set is imported from the typing module for type hints.

If you want to accept a list but ensure no duplicates, what should you do in FastAPI?

A Use Set as the type hint

B Use Dict instead

C Use List and manually check duplicates

D Use Tuple

Using Set automatically removes duplicates during validation.

What will FastAPI do if the client sends duplicates but the model expects a Set?

A Convert to a list

B Keep duplicates as is

C Raise a validation error

D Remove duplicates silently

FastAPI converts the input to a set, removing duplicates without error.

Explain how to validate a list and a set in FastAPI using Pydantic models.

Think about how Python types affect validation and data shape.

Describe a real-life example where you would prefer set validation over list validation in a FastAPI app.

Consider situations where duplicates cause problems.