Wtforms: How to generate blank value using select fields with dynamic choice values

Question

I'm using Flask with WTForms (doc) on Google App Engine. What is the best way to generate an field with an empty value for a select field?

form.group_id.choices = [(g.key().id(), g.name) for g in Group.all().order('name')]

Is there something like "blank=True" for the form field?

myfield = wtf.SelectField()

Answer 1

Can you just prepend an empty pair to the list?

form.group_id.choices.insert(0, ('', ''))

Answer 2

If it's a QuerySelectField, you can add parameters like this:

allow_blank=True, blank_text=u'-- please choose --'