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

问题

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()

回答1:

Can you just prepend an empty pair to the list?

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

回答2:

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

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

来源：https://stackoverflow.com/questions/5868718/wtforms-how-to-generate-blank-value-using-select-fields-with-dynamic-choice-val