How to set choices in dynamic with Django choicefield?
Similar to maersu's solution, but if you have a ModelForm with a model that has a ForeignKey to another model, you may want to assign to the field's queryset instead of choices.
I want to set choices in dynamic.
I used __set_choices method but, when request method is POST,
is_valid method always return False.

if request.method=='POST':
 _form = MyForm(request.POST)
 if _form.is_valid():
   #something to do