'Lists names of columns that have required fields.'

def get_required_columns(self):

    required_columns = []
    if self.formset_class:
        empty_form = self.get_formset().empty_form
        for column in self.columns.values():
            field = empty_form.fields.get(column.name)
            if (field and field.required):
                required_columns.append(column.name)
    return required_columns
