Flask isn't getting the checkbox value

Question

I am trying to print off the checkbox value in Flask when I hit the submit button.

app.py snippet:

@app.route('/test2', methods=['GET', 'POST'])
def test2():

    if request.method == "POST":
        if request.form['submit'] == 'submit':
            print(request.args.get('check'))

    return render_template('test.html')

HTML:

<div class="container"><br>
  <form role="form" method="post">
    <input type="checkbox" name="check" value="test">
    <button type="submit" name="submit" value="submit">Submit</button>
  </form>
</div>

It returns 'None' when I hit the submit button.

I have also tried request.form.get()

@app.route('/test2', methods=['GET', 'POST'])
def test2():

    if request.method == "POST":
        if request.form['submit'] == 'submit':
            print(request.form.get('check'))

    return render_template('test.html')

That also returns 'None'.

Solution

When submitting an HTML form, unchecked checkboxes do not send any data. On Flask's side, there will not be a key in form, since no value was received. If you want to check if a single checkbox (with a unique name) is checked, just test if it's name is in form. If you want to check which of multiple checkboxes (with the same name) are checked, use getlist instead.

One boolean:

<input type="checkbox" name="check">

checked = 'check' in request.form

Multiple options:

<input type="checkbox" name="check" value="1">
<input type="checkbox" name="check" value="2">
<input type="checkbox" name="check" value="3">

selected = request.form.getlist('check')
any_selected = bool(selected)