📓3.2: Flask HTTP Methods

Table of Contents

HTTP Methods in Flask Apps

In a Client-Server architecture, there is a set of rules, called a protocol, using which, we can allow the clients, to communicate with the server, and, vice-versa. Here, the Hyper Text Transfer Protocol (HTTP) is used, through which, communication is possible. The commonly used HTTP methods are: GET and POST.

For example: our browser passes our query to the Google server, then the Google server recieves and returns relevant suggestions.

HTTP Request Method
A request that tells a server what action to perform on a given resource.

Flask provides support for common HTTP methods such as GET, POST, PUT, DELETE, and others. These methods allow developers to build RESTful APIs and handle various types of client-server interactions. Below is an overview of HTTP methods supported in Flask, along with simple examples for each. Watch this for an overview.

POST Method for handling HTML forms

The POST method is used to send data to the server, typically to create or update resources. It is often used with forms or APIs.

Here is an example that demonstrates handling an HTML form and dynamically generating a page based on user responses.

An HTML page (such as index.html) page renders the form:

  <form action="/submit" method="POST">
      <!-- Text Input -->
      <label for="name">Name:</label>
      <input type="text" id="name" name="name" required><br><br>
  
      <!-- Age Input -->
      <label for="age">Age:</label>
      <input type="number" id="age" name="age" required><br><br>
  
      <!-- Dropdown Menu -->
      <label for="favorite_hobby">Favorite Hobby:</label>
      <select id="favorite_hobby" name="favorite_hobby" required>
          <option value="Reading">Reading</option>
          <option value="Sports">Sports</option>
          <option value="Gaming">Gaming</option>
          <option value="Cooking">Cooking</option>
          <option value="Traveling">Traveling</option>
      </select><br><br>
  
      <!-- Text Input -->
      <label for="favorite_color">Favorite Color:</label>
      <input type="text" id="favorite_color" name="favorite_color" required><br><br>
  
      <!-- Numerical Input -->
      <label for="lucky_number">Lucky Number:</label>
      <input type="number" id="lucky_number" name="lucky_number" required><br><br>
  
      <!-- Submit Button -->
      <button type="submit">Submit</button>
  </form>

Note the <form> attributes: action="/submit" and method="POST".

When the user clicks the button to submit the form, the data is sent to the /submit route in app.py:

  
  @app.route('/submit', methods=['POST'])
  def submit():
      # Collect form data
      user_data = {
          'name': request.form.get('name'),
          'age': request.form.get('age'),
          'favorite_color': request.form.get('favorite_color'),
          'favorite_hobby': request.form.get('favorite_hobby'),
          'lucky_number': request.form.get('lucky_number')
      }
      return render_template('result.html', user_data=user_data)

The /submit route processes the data and passes it to another template (here, result.html) for display. The user sees their submitted responses on the result page.

  
  {% extends 'layout.html' %}
  
  {% block content %}
  <p>Thank you for submitting your details! Here is what you entered:</p>
  <ul>
      <li><strong>Name:</strong> {{ user_data.name }}</li>
      <li><strong>Age:</strong> {{ user_data.age }}</li>
      <li><strong>Favorite Hobby:</strong> {{ user_data.favorite_hobby }}</li>
      <li><strong>Favorite Color:</strong> {{ user_data.favorite_color }}</li>
      <li><strong>Lucky Number:</strong> {{ user_data.lucky_number }}</li>
  </ul>
  <a href="/">Go Back</a>
  {% endblock %}

GET Method

The GET method is used to retrieve data from the server. It is the default method for routes in Flask and is typically used to fetch data without making changes on the server.

Example: 

@app.route('/get_example', methods=['GET'])
def get_example():
    param = request.args.get('param', 'default value')
    return f"Received parameter: {param}"
  • request.args.get('param') retrieves query parameters from the URL (e.g., /get_example?param=test).

PUT Method

The PUT method is used to update an existing resource or create a new one if it doesn’t exist.

Example: 

@app.route('/put_example/<resource_id>', methods=['PUT'])
def put_example(resource_id):
    data = request.json
    return f"Updated resource {resource_id} with data: {data}"
  • request.json retrieves JSON data sent in the body of the PUT request.
  • Typically, the resource ID is passed in the URL.

Example Request (Using cURL): 


curl -X PUT http://127.0.0.1:5000/put_example/1 -H "Content-Type: application/json" -d '{"key": "value"}'

DELETE Method

The DELETE method is used to delete a resource identified by the URL.

Example: 

@app.route('/delete_example/<resource_id>', methods=['DELETE'])
def delete_example(resource_id):
    return f"Deleted resource {resource_id}"
  • The resource ID is passed in the URL to identify which resource to delete.

Example Request (Using cURL): 


curl -X DELETE http://127.0.0.1:5000/delete_example/1

Summary of HTTP Methods

Method Description Use Case
GET Retrieve data Fetching resources
POST Send data to the server Creating resources
PUT Create or update a resource Updating entire resources
DELETE Delete a resource Removing resources
PATCH Partially update a resource Updating specific fields
HEAD Fetch metadata Checking resource headers
OPTIONS Discover allowed methods API method discovery
  • Use appropriate HTTP methods for their intended purpose to ensure your API adheres to RESTful principles.
  • Flask provides the flexibility to use methods in @app.route to handle multiple HTTP methods for a single route if needed.

Example for Multiple Methods: 


@app.route('/multi_example', methods=['GET', 'POST'])
def multi_example():
    if request.method == 'GET':
        return "This is a GET request"
    elif request.method == 'POST':
        return "This is a POST request"

Acknowledgement

Content on this page is adapted from .