HTML forms with POST method in Flask - Mini Project: Build & Apply

HTML Forms with POST Method in Flask

📖 Scenario: You are building a simple web page where users can submit their name and email address. The data will be sent securely to the server using the POST method.

🎯 Goal: Create a Flask app with an HTML form that uses the POST method to send user input to the server. The server should receive the data and store it in a dictionary.

📋 What You'll Learn

Create a Flask app with a route for the form page

Create an HTML form with method='POST' and input fields for name and email

Add a route to handle the POST request and store the submitted data in a dictionary

Display a confirmation message after submission

💡 Why This Matters

🌍 Real World

Websites often need forms to collect user information securely. Using POST method ensures data is sent safely to the server.

💼 Career

Understanding how to create and handle HTML forms with POST in Flask is essential for backend web development roles.

1

Set up Flask app and initial data storage

Create a Flask app by importing Flask and request from flask. Then create an empty dictionary called submissions to store user data.

Flask

from flask import Flask, request

# Your code here

Hint

Remember to import both Flask and request from the flask package.

2

Create HTML form with POST method

Add a route @app.route('/') with a function form() that returns an HTML form string. The form must have method='POST' and input fields with name='name' and name='email'. Include a submit button.

Flask

from flask import Flask, request

app = Flask(__name__)
submissions = {}

# Your code here

Hint

Use triple quotes ''' to return multi-line HTML as a string.

3

Handle POST request and store data

Modify the form() function to accept both GET and POST methods by adding methods=['GET', 'POST'] to the route. Inside the function, check if the request method is POST. If yes, get the name and email from request.form and store them in the submissions dictionary with name as the key and email as the value.

Flask

from flask import Flask, request

app = Flask(__name__)
submissions = {}

@app.route('/', methods=['GET', 'POST'])
def form():
    # Your code here

Hint

Use request.method == 'POST' to check the form submission.

4

Run the Flask app

Add the code to run the Flask app by checking if __name__ == '__main__' and calling app.run(debug=True).

Flask

from flask import Flask, request

app = Flask(__name__)
submissions = {}

@app.route('/', methods=['GET', 'POST'])
def form():
    if request.method == 'POST':
        name = request.form['name']
        email = request.form['email']
        submissions[name] = email
        return f"Thank you, {name}! Your email {email} has been recorded."
    return '''
    
      Name:
      
      Email:
      
      Submit
    
    '''

# Your code here

Hint

This code runs the Flask app when you start the script.

Practice

1. What does the POST method in an HTML form do in a Flask application?

easy

A. Automatically encrypts the form data before sending

B. Sends form data appended to the URL as query parameters

C. Prevents the form from submitting data

D. Sends form data inside the request body, not visible in the URL

Solution

1. Step 1: Understand HTTP methods in forms

   The POST method sends data inside the request body, keeping it hidden from the URL.

2. Step 2: Compare with GET method

   The GET method appends data to the URL, but POST does not, making it safer for sensitive data.

3. Final Answer:

   Sends form data inside the request body, not visible in the URL -> Option D

4. Quick Check:

   POST hides data in request body [OK]

Hint: POST sends data hidden in body, not URL [OK]

Common Mistakes:

• Confusing POST with GET method
• Thinking POST encrypts data automatically
• Believing POST prevents form submission

2. Which of the following is the correct way to specify a form that sends data using POST in HTML?

easy

A. ...

B. ...

C. ...

D. ...

Solution

1. Step 1: Identify the correct attribute for HTTP method

   The method attribute in the form tag defines how data is sent.

2. Step 2: Confirm correct value for POST

   Setting method='post' correctly configures the form to send data via POST.

3. Final Answer:

   <form method='post'>...</form> -> Option A

4. Quick Check:

   Use method='post' in form tag [OK]

Hint: Use method='post' attribute in form tag [OK]

Common Mistakes:

• Using 'action' instead of 'method' for HTTP method
• Writing method='get' when POST is needed
• Using non-standard attributes like 'send'

3. Given this Flask route and form, what will be printed when the form is submitted?

from flask import Flask, request
app = Flask(__name__)

@app.route('/submit', methods=['POST'])
def submit():
    name = request.form.get('name')
    return f'Hello, {name}!'

Send

medium

A. Hello, !

B. Hello, Alice!

C. Error: name not found

D. Hello, request.form!

Solution

1. Step 1: Understand form submission with POST

   The form sends the input named 'name' with value 'Alice' to the '/submit' route via POST.

2. Step 2: Check how Flask reads form data

   The route uses request.form.get('name') to get the value 'Alice' from the form data.

3. Final Answer:

   Hello, Alice! -> Option B

4. Quick Check:

   request.form.get('name') returns 'Alice' [OK]

Hint: request.form.get('name') reads POST form data [OK]

Common Mistakes:

• Using request.args instead of request.form for POST data
• Not specifying methods=['POST'] in route
• Missing the 'name' attribute in input

4. What is wrong with this Flask route that handles a POST form submission?

from flask import Flask, request
app = Flask(__name__)

@app.route('/login')
def login():
    username = request.form['username']
    return f'Welcome {username}'

medium

A. The route does not allow POST method, so form data won't be received

B. request.form['username'] should be request.args['username']

C. The route should use GET method instead of POST

D. Flask requires form data to be accessed via request.data

Solution

1. Step 1: Check route methods

   The route only allows GET by default, but form data sent by POST won't be processed.

2. Step 2: Confirm correct method usage

   To handle POST form data, the route must include methods=['POST'].

3. Final Answer:

   The route does not allow POST method, so form data won't be received -> Option A

4. Quick Check:

   Route must allow POST to read POST form data [OK]

Hint: Add methods=['POST'] to route decorator [OK]

Common Mistakes:

• Forgetting to add methods=['POST'] in route
• Using request.args for POST data
• Trying to access form data via request.data

5. You want to create a Flask route that accepts a POST form with fields 'username' and 'password'. It should return 'Login successful' only if username is 'admin' and password is 'secret', otherwise 'Login failed'. Which code snippet correctly implements this?

hard

A. from flask import Flask, request
app = Flask(__name__)

@app.route('/login', methods=['GET'])
def login():
user = request.form['username']
pwd = request.form['password']
if user == 'admin' and pwd == 'secret':
return 'Login successful'
else:
return 'Login failed'

B. from flask import Flask, request
app = Flask(__name__)

@app.route('/login')
def login():
user = request.args.get('username')
pwd = request.args.get('password')
if user == 'admin' and pwd == 'secret':
return 'Login successful'
else:
return 'Login failed'

C. from flask import Flask, request
app = Flask(__name__)

@app.route('/login', methods=['POST'])
def login():
user = request.form.get('username')
pwd = request.form.get('password')
if user == 'admin' and pwd == 'secret':
return 'Login successful'
else:
return 'Login failed'

D. from flask import Flask, request
app = Flask(__name__)

@app.route('/login', methods=['POST'])
def login():
user = request.form['username']
if user == 'admin':
return 'Login successful'
else:
return 'Login failed'

Solution

1. Step 1: Ensure route accepts POST method

   The route must specify methods=['POST'] to handle form POST data.

2. Step 2: Correctly read both 'username' and 'password' from request.form

   Use request.form.get() to safely get both fields and check their values.

3. Step 3: Implement correct login logic

   Return 'Login successful' only if both username and password match expected values; otherwise return 'Login failed'.

4. Final Answer:

   The code with methods=['POST'], request.form.get() for both fields, and checks both credentials -> Option C

5. Quick Check:

   from flask import Flask, request app = Flask(__name__) @app.route('/login', methods=['POST']) def login(): user = request.form.get('username') pwd = request.form.get('password') if user == 'admin' and pwd == 'secret': return 'Login successful' else: return 'Login failed' [OK]

Hint: Use methods=['POST'] and request.form.get for form fields [OK]

Common Mistakes:

• Using GET method instead of POST
• Reading form data from request.args
• Checking only username without password