Pre-populating a BooleanField as checked (WTForms)

If you have an object you can use it to populate your form like form = QuestionForm(obj=my_obj). If you only want to set the active attribute use form = QuestionForm(active=True).

A BooleanField defined like:

checkbox = BooleanField('title',
              default=True,
              render_kw ={'checked':''})

snahor's answer helped after much searching (+1). The google seems weak on this question. I found I needed

<div class="form-group">
  {{adminForm.is_admin.label}}
  {{adminForm.is_admin(checked=True, class_="form-control")}}
</div>

<div class="form-group">
  {{adminForm.is_admin.label}}
  {{adminForm.is_admin(checked=False, class_="form-control")}}
</div>

which I have utilised as

<div class="form-group">
  {{adminForm.is_admin.label}}
  {{adminForm.is_admin(checked=user.is_admin, class_="form-control")}}
</div>

To have the default boolean value as True, you need to set the default to "checked"

Basic fields Basic fields generally represent scalar data types with single values, and refer to a single input from the form.

class wtforms.fields.BooleanField(default field arguments, false_values=None)

Represents an input type="checkbox". Set the checked-status by using the default-option. Any value for default, e.g. default="checked" puts checked into the html-element and sets the data to True

Source

class QuestionForm(Form):
    question = TextField('Question', [validators.Required()])
    slug = TextField('Slug', [validators.Required()])
    active = BooleanField('Active', default="checked")