Pagination patterns in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this FastAPI pagination endpoint?

Consider this FastAPI endpoint that returns a paginated list of items. What will be the JSON response when requesting page=2 with size=3?

FastAPI

from fastapi import FastAPI, Query
from typing import List

app = FastAPI()

items = ["apple", "banana", "cherry", "date", "elderberry", "fig", "grape"]

@app.get("/items/")
async def get_items(page: int = Query(1, ge=1), size: int = Query(3, ge=1)) -> List[str]:
    start = (page - 1) * size
    end = start + size
    return items[start:end]

A ["banana", "cherry", "date"]

B ["date", "elderberry", "fig"]

C ["elderberry", "fig", "grape"]

D ["apple", "banana", "cherry"]

💡 Hint

Calculate the start and end indices for page 2 with size 3.

Page 2 with size 3 means items from index 3 to 5 (0-based). The items list sliced from 3 to 6 is ["date", "elderberry", "fig"].

📝 Syntax

intermediate

Which option correctly implements limit-offset pagination in FastAPI?

You want to implement limit-offset pagination in FastAPI. Which code snippet correctly returns the paginated items?

FastAPI

items = ["a", "b", "c", "d", "e", "f", "g"]

@app.get("/items/")
async def get_items(limit: int = 3, offset: int = 0):
    # return paginated items here

A return items[offset:offset+limit]

B return items[limit:offset+limit]

C return items[offset:limit]

D return items[limit:offset]

💡 Hint

Remember slicing syntax: list[start:end]

To get items starting at offset and up to limit count, slice from offset to offset+limit.

🔧 Debug

advanced

Why does this cursor pagination code raise an error?

This FastAPI cursor pagination code raises a TypeError. What is the cause?

FastAPI

from fastapi import FastAPI

app = FastAPI()

items = ["x", "y", "z"]

@app.get("/items/")
async def get_items(cursor: int = None, size: int = 2):
    start = cursor or 0
    end = start + size
    return items[start:end]

# Calling /items/?cursor=abc&size=2 causes the error

A The items list is empty causing an IndexError

B The code tries to add an int and a string causing a TypeError inside the function

C cursor is declared as int but receives a string, causing a validation error before the function runs

D The default value for cursor is None which cannot be used in arithmetic

💡 Hint

Check how FastAPI handles query parameter types.

FastAPI automatically validates query parameters. Passing 'abc' to an int parameter causes a validation error before the function executes.

🧠 Conceptual

advanced

What is a key advantage of cursor pagination over limit-offset pagination?

In FastAPI or any web API, why might you choose cursor pagination instead of limit-offset pagination?

A Cursor pagination avoids skipping or repeating items when data changes during pagination

B Cursor pagination is simpler to implement and requires less code

C Cursor pagination always returns the total count of items

D Cursor pagination allows random access to any page by number

💡 Hint

Think about data consistency when items are added or removed.

Cursor pagination uses a stable reference point, so it prevents skipping or duplicating items if the data changes while paginating.

❓ state_output

expert

What is the value of 'next_cursor' after this FastAPI cursor pagination call?

Given this code, what is the value of 'next_cursor' returned when calling /items/?cursor=1&size=2?

FastAPI

from fastapi import FastAPI
from typing import Optional

app = FastAPI()

items = ["a", "b", "c", "d", "e"]

@app.get("/items/")
async def get_items(cursor: Optional[int] = None, size: int = 2):
    start = cursor or 0
    end = start + size
    page_items = items[start:end]
    next_cursor = end if end < len(items) else None
    return {"items": page_items, "next_cursor": next_cursor}

A 2

B None

C 1

D 3

💡 Hint

Calculate end index and compare with list length.

Cursor=1, size=2 means start=1, end=3. Since 3 < 5 (length), next_cursor is 3.