Status Codes

An HTTP Status Code is used to help the Client (the user or system submitting data to the server) to understand what happened on the server side application.
Status Codes are international standards on how a Client/Server should handle the result of a request.
It allows everyone who sends a request to know if their submission was successful or not.

Status Codes Series and their meanings:

2xx Successful Status Codes:

4xx Client Errors Status Codes:

5xx Server Status Codes:

There are many more error codes which can find and can understand their meanings above one are the most common one.

HTTP Exceptions

Here we will use HTTP Exception package to highlight the error of file not found and will terminate the application.

Code:

from fastapi import FastAPI, Path, Query, HTTPException
from books3 import Book
from datavalidatorhelper import BookRequest

app = FastAPI()

BOOKS = [
    Book(id=1, title="DSA with Java", 
         author="Puneet Kumar Singh", 
         description="A comprehensive guide to Data Structures 
and Algorithms using Java.", 
         rating=5,
         published_date=2014),
    Book(id=2, title="Python Programming", 
         author="Puneet Kumar Singh", 
         description="An introduction to Python programming for beginners.", 
         rating=4,
         published_date=2015),
    Book(id=3, title="Machine Learning Basics", 
         author="Puneet Kumar Singh", 
         description="Understanding the fundamentals of Machine Learning.", 
         rating=4,
         published_date=2014),
    Book(id=4, title="Web Development with FastAPI", 
         author="Ramesh Jha", 
         description="Building web applications using FastAPI.", 
         rating=3,
         published_date=2016),
    Book(id=5, title="Data Science with Python", 
         author="Kalidas", 
         description="A guide to Data Science using Python.", 
         rating=2,
         published_date=2018),
    Book(id=6, title="Advanced Java Programming", 
         author="Kalpana Gupta", 
         description="Deep dive into advanced concepts of Java programming.", 
         rating=1,
         published_date=2014)
]

# API endpoint to get all books detail unfiltered.
@app.get("/books") # static path to get all books
async def read_all_books():
    """
    This function returns the list of all books.
    """
    return BOOKS

""" post request without any input validation 
@app.post("/create_book")
async def create_book(book_request=Body()):
    BOOKS.append(book_request)
"""
#API endpoint to fetch book by using published_date as parameter
@app.get("/books/published/")
async def read_book_by_published_date(published_date: int = Query(gt=1999, lt=2031)): 
    # contraints check at the time of input
    books_to_return = []
    for book in BOOKS:
        if book.published_date == published_date:
            books_to_return.append(book)
    return books_to_return

# API endpoint to fetch book by using id
@app.get("/books/{book_id}")
async def read_book_by_id(book_id: int = Path(gt=0)): 
# it will make sure that index will start from 1.
    for book in BOOKS:
        if book.id == book_id:
            return book
    raise HTTPException(status_code=404, detail='Item not found')

# API endpoint to fetch books by rating
@app.get("/books/")
async def read_book_by_rating(rating: int = Query(gt=0, lt=6)): 
# contraints check at the time of input
    book_to_return = []
    for book in BOOKS:
        if book.rating == rating:
            book_to_return.append(book)
    return book_to_return

#post request with input validator
@app.post("/creat_book")
async def create_book(book_request: BookRequest):
    new_book = Book(**book_request.model_dump()) 
# new_book = Book(**book_request.dict()) -> if you are using pydantic 
version 1 else the model_dump() for pydentic version 2.
    # BOOKS.append(new_book) -> it will store the valid 
input dump but you can have duplicate ids.
    BOOKS.append(find_book_id(new_book)) 
# It will add latest id sequence number to id automatically and will 
overwrite the provided input so you don't need to bother about the id value sequence.

def find_book_id(book: Book):
    if len(BOOKS) > 0:
        book.id = BOOKS[-1].id + 1
    else:
        book.id = 1
    return book


# API endpoint to update existing book entry
@app.put("/books/update_book")
async def update_book_by_id(book_request: BookRequest):
    book_changed = False
    new_book=Book(**book_request.model_dump())
    for i in range(len(BOOKS)):
        if BOOKS[i].id == new_book.id:
            BOOKS[i]=new_book
            book_changed = True
            return {"message": "Book is updated", "detail": new_book}
    if not book_changed:
        raise HTTPException(status_code=404, detail="Item not found")

# API endpoint to delete book entry from library
@app.delete("/books/{book_id}")
async def delete_book_by_id(book_id : int = Path(gt=0)): 
# it will make sure that index will start from 1.
    book_changed = False
    for i in range(len(BOOKS)):
        if BOOKS[i].id == book_id:
            BOOKS.pop(i)
            book_changed = True
            return {"message": "Book is deleted successfully."}
    if not book_changed:
        raise HTTPException(status_code=404, detail="Item not found")

Result:

Read by book_id

Delete by book_id

Update by book_id

Explicit Status Code Responses

With the help of starlette we can explicitly provide status code to our app endpoints at successful operations. As we can provide right response code which will help to standardize the response.

code:

from fastapi import FastAPI, Path, Query, HTTPException
from books3 import Book
from datavalidatorhelper import BookRequest
from starlette import status

app = FastAPI()

BOOKS = [
    Book(id=1, title="DSA with Java", 
         author="Puneet Kumar Singh", 
         description="A comprehensive guide to Data 
Structures and Algorithms using Java.", 
         rating=5,
         published_date=2014),
    Book(id=2, title="Python Programming", 
         author="Puneet Kumar Singh", 
         description="An introduction to Python programming for beginners.", 
         rating=4,
         published_date=2015),
    Book(id=3, title="Machine Learning Basics", 
         author="Puneet Kumar Singh", 
         description="Understanding the fundamentals of Machine Learning.", 
         rating=4,
         published_date=2014),
    Book(id=4, title="Web Development with FastAPI", 
         author="Ramesh Jha", 
         description="Building web applications using FastAPI.", 
         rating=3,
         published_date=2016),
    Book(id=5, title="Data Science with Python", 
         author="Kalidas", 
         description="A guide to Data Science using Python.", 
         rating=2,
         published_date=2018),
    Book(id=6, title="Advanced Java Programming", 
         author="Kalpana Gupta", 
         description="Deep dive into advanced concepts of Java programming.", 
         rating=4,
         published_date=2014)
]

# API endpoint to get all books detail unfiltered.
@app.get("/books", status_code=status.HTTP_200_OK) # static path to get all books
async def read_all_books():
    """
    This function returns the list of all books.
    """
    return BOOKS

""" post request without any input validation 
@app.post("/create_book")
async def create_book(book_request=Body()):
    BOOKS.append(book_request)
"""
#API endpoint to fetch book by using published_date as parameter
@app.get("/books/published/", status_code=status.HTTP_200_OK)
async def read_book_by_published_date(published_date: int = Query(gt=1999, lt=2031)): 
    # contraints check at the time of input
    book_present = False
    books_to_return = []
    for book in BOOKS:
        if book.published_date == published_date:
            books_to_return.append(book)
            book_present = True
    if not book_present:
        raise HTTPException(status_code=404, detail="Item not found")
    else:
        return books_to_return

# API endpoint to fetch book by using id
@app.get("/books/{book_id}", status_code=status.HTTP_200_OK)
async def read_book_by_id(book_id: int = Path(gt=0)): 
# it will make sure that index will start from 1.
    for book in BOOKS:
        if book.id == book_id:
            return book
    raise HTTPException(status_code=404, detail='Item not found')

# API endpoint to fetch books by rating
@app.get("/books/", status_code=status.HTTP_200_OK)
async def read_book_by_rating(rating: int = Query(gt=0, lt=6)): 
# contraints check at the time of input
    book_found = False
    book_to_return = []
    for book in BOOKS:
        if book.rating == rating:
            book_to_return.append(book)
            book_found = True
    if not book_found:
        raise HTTPException(status_code=404, detail="Item not found")
    else:
        return book_to_return

#post request with input validator
@app.post("/creat_book", status_code=status.HTTP_201_CREATED)
async def create_book(book_request: BookRequest):
    new_book = Book(**book_request.model_dump()) 
# new_book = Book(**book_request.dict()) -> if you are using
 pydantic version 1 else the model_dump() for pydentic version 2.
    # BOOKS.append(new_book) -> it will store the valid input 
dump but you can have duplicate ids.
    BOOKS.append(find_book_id(new_book)) 
# It will add latest id sequence number to id automatically 
and will overwrite the provided input so you don't need to 
bother about the id value sequence.

def find_book_id(book: Book):
    if len(BOOKS) > 0:
        book.id = BOOKS[-1].id + 1
    else:
        book.id = 1
    return book


# API endpoint to update existing book entry
@app.put("/books/update_book", status_code=status.HTTP_204_NO_CONTENT)
async def update_book_by_id(book_request: BookRequest):
    book_changed = False
    new_book=Book(**book_request.model_dump())
    for i in range(len(BOOKS)):
        if BOOKS[i].id == new_book.id:
            BOOKS[i]=new_book
            book_changed = True
    if not book_changed:
        raise HTTPException(status_code=404, detail="Item not found")

# API endpoint to delete book entry from library
@app.delete("/books/{book_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_book_by_id(book_id : int = Path(gt=0)): 
# it will make sure that index will start from 1.
    book_changed = False
    for i in range(len(BOOKS)):
        if BOOKS[i].id == book_id:
            BOOKS.pop(i)
            book_changed = True
            break
    if not book_changed:
        raise HTTPException(status_code=404, detail="Item not found")