HTML forms with POST method in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when this Flask route receives a POST request?

Consider this Flask route handling a form submission with POST method. What will be the output if the form sends 'username' as 'alice'?

Flask

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

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

A Hello, None!

B Hello, alice!

C Method Not Allowed error

D Internal Server Error

💡 Hint

Remember that request.form contains data sent by POST method from the form.

The route accepts POST requests and extracts 'username' from form data. If the form sends 'alice', the response is 'Hello, alice!'.

📝 Syntax

intermediate

Which option correctly defines a Flask route to handle POST form data?

Select the option that correctly defines a Flask route to accept POST requests and retrieve a form field named 'email'.

A

@app.route('/email')
def email():
    email = request.form['email']
    return email

B

@app.route('/email', methods=['POST'])
def email():
    email = request.args['email']
    return email

C

@app.route('/email', methods=['GET'])
def email():
    email = request.form['email']
    return email

D

@app.route('/email', methods=['POST'])
def email():
    email = request.form['email']
    return email

💡 Hint

POST data is accessed via request.form, and the route must allow POST method.

Option D correctly sets methods=['POST'] and accesses form data with request.form['email']. Others either miss POST method or use wrong data source.

🔧 Debug

advanced

Why does this Flask form submission always return 'None' for the username?

Given this Flask route and HTML form, why does the server always respond with 'Hello, None!' even when a username is entered?

Flask

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

@app.route('/login', methods=['POST'])
def login():
    username = request.args.get('username')
    return f"Hello, {username}!"

# HTML form:
# <form action="/login" method="post">
#   <input type="text" name="username">
#   <input type="submit">
# </form>

A Because request.args is used instead of request.form to get POST data.

B Because the form method should be GET, not POST.

C Because the input field is missing a 'value' attribute.

D Because the route does not return a valid string.

💡 Hint

POST form data is in request.form, not request.args.

request.args contains query parameters from URL (GET data). POST form data is in request.form. Using request.args.get('username') returns None.

❓ state_output

advanced

What is the value of 'count' after submitting the form twice?

This Flask app counts how many times the form is submitted. What will be the value of 'count' after two POST submissions?

Flask

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

count = 0

@app.route('/submit', methods=['POST'])
def submit():
    global count
    count += 1
    return f"Submission count: {count}"

A Submission count: 0

B Submission count: 1

C Submission count: 2

D UnboundLocalError

💡 Hint

The global variable 'count' is incremented on each POST request.

The global 'count' variable increments by 1 on each POST. After two submissions, count is 2.

🧠 Conceptual

expert

Which statement about HTML forms with POST method and Flask is TRUE?

Select the true statement about handling HTML forms with POST method in Flask.

A To handle POST data, the Flask route must specify methods=['POST'] or methods=['GET', 'POST'].

B Flask automatically parses JSON data sent by POST forms into request.form.

C Form data sent by POST is accessible via request.args in Flask.

D Flask's request.form only contains data sent by POST method, never by GET.

💡 Hint

Check how Flask routes handle HTTP methods and where form data is stored.

Flask's request.form contains POST form data, but request.args contains GET query parameters. The route must allow POST method explicitly. JSON data is accessed via request.get_json(), not request.form.