Why HTTP methods (GET, POST, PUT, DELETE) in Flask? - Purpose & Use Cases

The Big Idea

Discover how simple rules for web actions can save you hours of messy code and bugs!

The Scenario

Imagine building a web app where you manually handle every user action like fetching data, sending forms, updating info, or deleting items by writing separate code for each without clear rules.

The Problem

Manually managing these actions gets confusing fast, leads to messy code, and makes it hard to keep track of what each part does. It's easy to mix up how data is sent or received, causing bugs and security issues.

The Solution

HTTP methods like GET, POST, PUT, and DELETE give clear, standard ways to handle different actions in web apps. Using them with Flask routes organizes your code, making it easier to read, maintain, and secure.

Before vs After

✗ Before

def handle_request():
    if 'fetch' in request.args:
        # fetch data
    elif 'send' in request.args:
        # send data
    elif 'update' in request.args:
        # update data
    elif 'remove' in request.args:
        # delete data

✓ After

@app.route('/item', methods=['GET', 'POST', 'PUT', 'DELETE'])
def item():
    if request.method == 'GET':
        # fetch data
    elif request.method == 'POST':
        # send data
    elif request.method == 'PUT':
        # update data
    elif request.method == 'DELETE':
        # delete data

What It Enables

This lets you build clear, reliable web apps where each action has its own place, making your app easier to develop, test, and grow.

Real Life Example

Think of an online store: customers browse products (GET), add items to cart (POST), change quantities (PUT), or remove items (DELETE). HTTP methods help organize these actions cleanly.

Key Takeaways

Manual handling of web actions is confusing and error-prone.

HTTP methods provide a clear, standard way to manage different actions.

Using them in Flask routes makes your code organized and easier to maintain.

Practice

1. Which HTTP method is typically used in Flask to retrieve data without changing anything on the server?

easy

A. PUT

B. POST

C. GET

D. DELETE

Solution

1. Step 1: Understand HTTP methods purpose

   GET is used to request data without modifying it, so it is safe and idempotent.

2. Step 2: Match method to Flask usage

   In Flask, GET routes are used to send data back to the client without changing server state.

3. Final Answer:

   GET -> Option C

4. Quick Check:

   Retrieve data = GET [OK]

Hint: GET reads data, POST creates, PUT updates, DELETE removes [OK]

Common Mistakes:

• Confusing POST with GET for data retrieval
• Using DELETE to get data
• Thinking PUT is for reading data

2. Which of the following Flask route definitions correctly allows handling both GET and POST methods?

easy

A. @app.route('/submit', allow_methods=['GET', 'POST'])

B. @app.route('/submit', methods=['GET', 'POST'])

C. @app.route('/submit', methods='GET, POST')

D. @app.route('/submit', method=['GET', 'POST'])

Solution

1. Step 1: Recall Flask route syntax for methods

   Flask uses the 'methods' keyword argument as a list of strings to specify allowed HTTP methods.

2. Step 2: Check each option's syntax

   @app.route('/submit', methods=['GET', 'POST']) correctly uses methods=['GET', 'POST']. Others have wrong keywords or wrong data types.

3. Final Answer:

   @app.route('/submit', methods=['GET', 'POST']) -> Option B

4. Quick Check:

   Correct keyword and list format = @app.route('/submit', methods=['GET', 'POST']) [OK]

Hint: Use methods=['GET', 'POST'] exactly in route decorator [OK]

Common Mistakes:

• Using 'method' instead of 'methods'
• Passing methods as a string instead of list
• Using unknown keywords like 'allow_methods'

3. What will be the output when a client sends a DELETE request to this Flask route?

@app.route('/item/', methods=['DELETE'])
def delete_item(id):
    return f"Deleted item {id}", 200

medium

A. "Deleted item <id>" with status 200

B. 404 Not Found error

C. Method Not Allowed error

D. Empty response with status 204

Solution

1. Step 1: Analyze route and method

   The route accepts DELETE requests with an integer id parameter and returns a string with status 200.

2. Step 2: Understand response for DELETE request

   Since the method matches and function returns a message with 200, the client receives that message and status.

3. Final Answer:

   "Deleted item <id>" with status 200 -> Option A

4. Quick Check:

   DELETE request handled correctly = "Deleted item <id>" with status 200 [OK]

Hint: Route method matches request method, so response is returned [OK]

Common Mistakes:

• Expecting 404 if route exists
• Confusing DELETE with GET behavior
• Assuming empty response without checking code

4. Identify the error in this Flask route that should handle PUT requests:

@app.route('/update', methods=['PUT'])
def update():
    data = request.get_json()
    return 'Updated', 200

medium

A. Missing import of 'request' from Flask

B. Incorrect HTTP method name 'PUT'

C. Route decorator syntax is invalid

D. Function must return JSON, not string

Solution

1. Step 1: Check usage of 'request'

   The function uses 'request.get_json()' but 'request' is not imported from Flask, causing a NameError.

2. Step 2: Verify other parts

   Method 'PUT' is valid, route syntax is correct, and returning string with status 200 is allowed.

3. Final Answer:

   Missing import of 'request' from Flask -> Option A

4. Quick Check:

   Using 'request' without import causes error [OK]

Hint: Always import 'request' to access request data [OK]

Common Mistakes:

• Forgetting to import 'request'
• Thinking PUT is invalid method
• Assuming string return is wrong

5. You want to create a Flask API endpoint to update a user's email using PUT and delete the user using DELETE at the same URL '/user/'. Which is the best way to define this in Flask?

hard

A. Use GET method for both update and delete actions

B. Create two separate routes with different URLs for PUT and DELETE

C. Use only POST method and check a hidden field for action

D. Use one route with methods=['PUT', 'DELETE'] and check request.method inside the function

Solution

1. Step 1: Understand RESTful design

   PUT and DELETE are standard methods for update and delete at the same resource URL.

2. Step 2: Implement in Flask

   Flask allows one route to handle multiple methods; inside the function, you check request.method to run correct code.

3. Final Answer:

   Use one route with methods=['PUT', 'DELETE'] and check request.method inside the function -> Option D

4. Quick Check:

   Multiple methods on one route with method check = Use one route with methods=['PUT', 'DELETE'] and check request.method inside the function [OK]

Hint: One route, multiple methods, check request.method inside [OK]

Common Mistakes:

• Creating separate URLs for same resource actions
• Using POST or GET incorrectly for update/delete
• Not checking request.method inside route