How to dynamically set default value in WTForms RadioField?

Question

I\'m building a website with the Python Flask framework in which I use WTForms. In one form I\'ve got a RadioField defined as follows:

display = RadioField(\         


        

Answer 1

You need to run myForm.process() after adding the choices and setting the default property:

myForm = MyForm()
myForm.display.choices = [('ONE', 'one'), ('TWO', 'two')]
myForm.display.default = 'ONE'
myForm.process() # process choices & default

This is because the default is propagated to the field value (and, in the case of RadioField, the checked property) in the process method, which is called in the constructor.