Lazy Iterator to populate WTForms choices

lazy.py

class LMSInstanceIterator(object):
    """Lazy iterator to populate ClientEditForm.lms_instance when rendered"""
    def __iter__(self):
        return iter([(instance.key.id(), instance.name)
                     for instance in lmsinstances.query()])
                     
class ClientEditForm(BaseForm):
    lms_instance = fields.SelectField('LMS Instance', choices=LMSInstanceIterator())