Validator for part of a schema, ignoring some fields

    :param schema: the Schema
    :param filtered_fields: fields to filter out

def partial_schema(schema, filtered_fields):
    """
    Validator for part of a schema, ignoring some fields

    :param schema: the Schema
    :param filtered_fields: fields to filter out
    """
    return Schema({
        k: v for k, v in schema.schema.items()
        if getattr(k, 'schema', k) not in filtered_fields
    }, extra=ALLOW_EXTRA)