def _get_free_field_name(self, field):
        "Generate an available name for a field"
        num = 0
        field_name = unicode(field.name) + u"___" + unicode(num)
        while field_name not in self.fields:
            num += 1
            field_name = unicode(field.name) + u"___" + unicode(num)
        return field_name
dataset/ETHPy150Open treeio/treeio/treeio/identities/forms.py/ContactForm._get_free_field_name/operator `in` -> `not in`