FastApi-playground

A FastAPI lab for prototyping ideas, testing features, and deepening API knowledge.

Why FastAPI is fast to code?

1. Automatic input Validation
   
2. Auto-Generated interactive Documentation
   
3. Seamless Integration with Modern Ecosystem (ML/DL libraries, OAuth, JWT, SQL Alchemy, Docker, Kubernetes etc)

Run the Server:

uvicorn main:app --reload
fastapi dev main.py

To run ML_Project

cd ML_Project/
fasapi dev app.py

Request body:

A request body is the portion of an HTTP request that contains data sent by the client to the server. It is typically used to HTTP methods POST or PUT to transmit structured data (e.g. JSON, XML, form-data) for the purpose of creating or updating resources on the server. The server parses the request body to extract the necessary information and perform the intended operation.

HTTP Requests:

Real-world analogy:

GET is like reading a book in a library. Post is like writing a note and handing it to the librarian.

• When you GET, you’re just requesting to see something
• When you POST, you’re sending data to be processed or saved.

Technical Difference

Feature	GET	POST
Purpose	Retrieve data	Submit data
Data location	In URL (query string)	In the request body
Visibility	Data is visible in URL	Data is hidden from URL
Use for	Reading/fetching resources	Creating/updating resources
Bookmarkable	Yes	No
Idempotent	Yes (repeating gives same result)	Not necessarily (can cause changes

Get request:

GET /search?query=shoes HTTP/1.1

• You’re asking: “Hey server, show me all the shoes.”

POST request:

POST /add-to-cart HTTP/1.1
Body: { “item_id”: 123, “quantity”: 2}

• You’re saying: “Hey server, please add this item to my cart.”

Think of it like a conversation with a website:

1. GET = “Just give me info”

• You’re asking the server for something.
• Example: “Show me all blog posts tagged with ‘travel’.”
• You don’t change anything on the server.
• The server responds with that info.

**In the browser: **

• You type in a URL or click a link – that’s a GET request.
• Example: https://example.com/posts?tag=travel

2. POST = “I’m giving you something to do”

• You’re sending data to the server to do something with it.
• Example: “Here is my comment on this blog post.”
• The server might save that comment to a database.

**In the browser: **

• You fill out a form and click “Submit” – that’s a POST request.
• Example: You post a review, submit login info, or upload a photo.

Why does it matter?

• GET is for viewing. (safe, can be cached, can be bookmarked.)
• POST is for doing. (Sends new data, not cached, not bookmarkable.)

GET Scenarios (Read-only actions)

These are situations where the client just wants to retrieve data, without making any changes:

1. Loading a web page

• URL: https://news.com/latest
• You want to view the latest news.
• No data is sent except in the URL.

2. Search queries

• URL: https://store.com/search?q=laptop
• You are searching for laptop”.
• The search term is passed as a query string.

3. Viewing a user profile

• URL: https://site.com/user/john
• Just displays John’s profile
• Doesn’t change anything.

4. Pagination

• URL: https://blog.com/posts?page=3
• You’re just asking for page 3 of the blog.

5. Filtering results

• URL: https://shop.com/products?category=shoes&price=low
• You’re applying filters to what you see.

POST Scenarios (Write/Submit actions)

These are situations where the client is sending data to the server to create, modify, or trigger actions.

1. Submitting a login form

• URL: https://site.com/login
• Sends your username and password.
• Server checks and starts your session.

2. Creating a new user/account

• URL: https://site.com/signup
• Sends your name, email, password, etc.

3. Submitting a contact form

• Sends message, name, email to the server to be saved or emailed.

4. Uploading a file or image

• Sends the file data as part of the request body.

5. Adding to a shopping cart

• You click “Add to Cart” – the item ID and quantity are sent to the server.

6. Placing an order

• URL: https://shop.com/checkout
• Sends the cart items, payment detail, shipping info.

7. Posting a comment or message

• Submits text, maybe with a post ID or thread ID.

Summary Table:

Scenario	Method
View a blog post	GET
Search for a products	GET
Login to a site	POST
Sign up for a new account	POST
Add an item to cart	POST
Submit a contact form	POST
View a list of product	GET
Filter products by price	GET
Post a review	GET
Get weather info by city	GET
Upload a profile picture	POST
View user profile	GET

GET Request on Flipkart (Viewing or fetching data)

These happen when you’re just browsing or searching without changing anything on the server.

1. Homepage Load

• When you go to https://www.flipkart.com, your browser sends a GET request.
• You’re just asking to view the homepage.

2. Searching for a product

• You type “mobile phone” in the search bar and hit Enter.
• URL becomes: https://www.flipkart.com/search?q=mobile+phones
• That’s a GET request with the query q=mobile+phones
• You are just requesting info.

3. Filtering products

• Apply a filter like “Price: Low to High” or select a brand.
• URL updates to something like: https://www.flipkart.com/search?q=mobile+phones&sort=price_asc&brand=Samsung
• Still a GET request – just showing filtered results.

4. Viewing a product

• Click on a phone to see its details.
• URL: https://www.flipkart.com/Samsung-galaxy/product-id
• Again, it’s just fetching info – so it’s a GET.

POST Requests on Flipkart (Sending data or changing state)

These happen when you interact in a way that changes something – like logging in, adding to cart, or checking out.

1. Logging in

• You enter your phone/email and password.
• Your browser sends a POST request to https://www.flipkart.com/api/login
• Flipkart checks your credentials and starts a session.

2. Adding a product to cart

• You click “Add to Cart”.
• A POST request is sent to something like: https://www.flipkart.com/api/add-to-cart
• Data sent: { product_id: 12345, quantity: 1 }

3. Placing an order

• After selecting items, address, and payment, you click “Place Order”.
• A POST request sends your order details to Flipkart’s servers to process.

4. Submitting a review

• You rate a product and write a review.
• Flipkart uses a POST request to store that review in their database.

Path Parameter

The Path() function in FastAPI is used to provide, validation rules, and documentation hints for path parameters in your API endpoints.

Title
Description
ge, gt, le, lt
Min_length
Max_length
regex

HTTP status codes

HTTP status codes are 3-digit number returned by a web server (like FastAPI) to indicate the result of a client's request (like from a browser or API consumer).

LINK

They help the client (browser, fronted, mobile app, etc.) understand:

• whether the request was successful.
• whether something went wrong.
• and what kind of issue occurred (if any).

2xx	✅ Success	The request was successfully recieved and processed
3xx	🔁 Redirection	Further action needs to be taken (e.g. redirect)
4xx	⚠️ Client Error	Something is wrong with the request from the client
5xx	❌ Server Error	Something went wrong on the server side

200 OK	Standard success	A GET or POST suceeded
201 Created	Resource created	After a POST that created something
204 No Content	Success, but no data returned	After a DELETE request
400 Bad Unauthorized	Malformed or invalid authentication	Missing field, wrong data type
401 Unauthorized	No/invallid authentication	Login required
403 Forbidden	Authenticated, but no permission	Logged in but not allowed
404 Not Found	Resource doesn't exist	Patient ID not DB
500 Internal Server Error	Generic failure	Something broken the server
502 Bad Gateway	Gateway (like Nginx) failed to reach backend
503 Service Unavailable	Server is down or overloaded

HTTPException is a Special built-in exception in FastAPI used to return custom HTTP error responses when something goes wrong your API.

Instead of returning a normal JSON or crashing the Server, you can gracefully raise an error with:

• a proper HTTP stats code (like 404, 400, 403, etc.)
• a custom error message
• (optional) extra header

Query Parameter

Query parameter are optional key-value pairs appended to the end of a URL, used to pass additional data to the server in an HTTP request. They are typically employed for operations like filtering , sorting.
searching and pagination without altering the endpoint path itself.

/patients?city=Delhi&sort_by=age

• The ? marks the start of query parameters.
• Each parameter is a key-value pair: key=value
• Multiple parameters are separated by &

In this case:

• city=Delhi is query parameter for filtering
• sort_by=age is a query parameter for sorting

Query() is a utility function provided by FastAPI to declare, validate, and document query parameters in your API endpoints.

Pydantic

1. Define a Pydantic model that represents the ideal schema of the data.

• This includes the expected fields, their types, and any validation constraints (e.g. gt=0 for positive number).

2. nstantiate the model with raw input data (Usually a dictionary or JSON-like structure).

• Pydantic will Automatically validate the data and coerce it into the correct Python type (if possible).
• If the data doesn't meet the model's requirements, Pydantic raise a validationError.

3. Pass the validateed model object to functions or use it throughout your codebase.

• This ensures that every part of your program works with clean, type-safe, and logically valid data.

What is the difference between class and function in Python?

In Python, you use classes to describe objects. Think of a class as a tool you use to create your own data structures that contain information about something; you can then use functions (methods) to perform operations on the data you describe.

Bash Environment Commands

• To Create a file

touch <file_name>
# Example: touch Test_Excercise.py

• Run python (.py) file:

python file_name.py

• To Create a virtual environment

python -m venv <env_name>
# Example: python -m venv playground

• Activate the virtual environment

source <env_name>/bin/activate  # for macos
source <env_name>/Scripts/activate  # for windows
# Example for macos: source playground/bin/activate
# Example for window bash: source playground/Scripts/activate

• Deactivate the virtual environment

deactivate

• Delete the environment

rm -rf <env_name>
# Example: rm -rf playground

• Useful Bash Tips for Environment Management

List Python virtual environments if stored in a folder (e.g., ~/venvs)

ls ~/venvs

Find all virtual environments on your system (search for activate scripts)

find ~ -type f -name "activate"

Quick script to list venv env names inside ~/venvs

for dir in ~/venvs/*; do
  if [ -f "$dir/bin/activate" ]; then
    echo "$(basename "$dir")"
  fi
done

Pip Commands

• To install requirements.txt = pip install -r requirements.txt
• To check install packages = pip list
• To check detailed about package = pip show package_name
• To install package = pip install package_name
• To uninstall package = pip uninstall package_name
• To save all packages of env to a requirements.txt file = pip freeze > requirements.txt

Git commands

• To add all file = git add .
• To add any particular file = git add <file_name>
• To commit = git commit -m "commit message"
• To push the code = git push origin main

Docs:

• Documentation: https://fastapi.tiangolo.com

• Source Code: https://github.com/fastapi/fastapi

• Swagger UI:

localhost:8000/docs
http://127.0.0.1:8000/docs