def utf8(string):
    """
    Make sure string is utf8 encoded bytes.

    If parameter is a object, object.__str__ will been called before encode as bytes
    """
    if isinstance(string, six.text_type):
        return string.encode('utf8')
    elif isinstance(string, six.binary_type):
        return string
    else:
        return six.text_type(string).encode('utf8')

    Make sure string is utf8 encoded bytes.

    If parameter is a object, object.__str__ will been called before encode as bytes
    
pyspider/libs/utils.py