BooleanField does not honor default value

[Ademaro]

I'm having issues with rendering a BooleanField correctly

from flask_wtf import FlaskForm
from wtforms import BooleanField

class TestForm(FlaskForm):
    check = BooleanField("mycheckbox", default="checked")

But it renders unchecked...

Works correctly if written like this:

class TestForm(FlaskForm):
    check = BooleanField("mycheckbox", render_kw={"checked": True})

Environment: MacOS 12.0.1

• Python version: 3.9.8
• Flask-WTF version: 0.15.1
• Flask version: 2.0.2

[David Lord]

Presumably it should be default=True.

[Ademaro]

@davidism In general, it does not matter, but I tried with your version, the effect is the same...

[jnnkB]

I just tested it using the same environment and this code and it worked fine.

from flask import Flask
from flask_wtf import FlaskForm
from wtforms import BooleanField


app = Flask(__name__)
app.secret_key = "VERY SECURE"

class TestForm(FlaskForm):
    check = BooleanField("mycheckbox", default="checked")
    check2 = BooleanField("mycheckbox", default=True)


@app.route("/")
def index():
    form = TestForm()
    return form.check() + form.check2()

This is the result:

<input checked id="check" name="check" type="checkbox" value="y"><input checked id="check2" name="check2" type="checkbox" value="y">⏎

[Ademaro]

My variant not worked about this line: form = TestForm(request.form)

from flask import Flask, request
from flask_wtf import FlaskForm
from wtforms import BooleanField


app = Flask(__name__)
app.secret_key = "VERY SECURE"


class TestForm(FlaskForm):
    check = BooleanField("mycheckbox", default="checked")
    check2 = BooleanField("mycheckbox", default=True)


@app.route("/")
def index():
    form = TestForm(request.form)
    return form.check() + form.check2()

Now all good, thanks)

# ...
if request.method == 'POST':
    form = TestForm(request.form)
else:
    form = TestForm()

[jnnkB]

Just a short note: flask-wtf provides validate_on_submit which checks the request method and validates the data. So if you do not intend to skip validation its probably good yo use this method. Here is a small code example:

@app.route('/submit', methods=['GET', 'POST'])
def submit():
    form = MyForm()
    if form.validate_on_submit():
        return redirect('/success')
    return render_template('submit.html', form=form)

[Ademaro]

@jnnkB Thanks, but in your example, saving the filled form fields after submitting the form, if errors occur in any of the fields, will not work in your example. Previously, I always passed the request.form to the constructor of the form class:

form = MyForm(request.form)

But this stopped working with checkboxes, so I had to make an additional check:

if request.method == 'POST':
    form = MyForm(request.form)
else:
    form = MyForm()

After these checks, of course, the real code contains if form.validate_on_submit ():.

I don't know how much better it can be done, but for now, like this...