Pre-populating a BooleanField as checked (WTForms)

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>

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).