This question is hard to answer because it lacks context. What exactly are you trying to do? It appears what you are trying to do is subclass a form. In that case, here is an example.
class ProfileForm(Form):
birthday = DateTimeField('Your Birthday', format='%m/%d/%y')
signature = TextAreaField('Forum Signature')
class AdminProfileForm(ProfileForm):
username = StringField('Username', [validators.Length(max=40)])
level = IntegerField('User Level', [validators.NumberRange(min=0, max=10)])
What's happening here is the AdminProfileForm is assuming the values of ProfileForm. Calling one AdminProfileForm then generates all the fields for both.