'Constructor.
We only accept str instances.
Args:
arg: optional str instance (default \'\')'

def __new__(cls, arg=None):

    if (arg is None):
        arg = ''
    if isinstance(arg, str):
        return super(_BaseByteType, cls).__new__(cls, arg)
    raise TypeError(('%s()    argument    should    be    str    instance,    not    %s' % (cls.__name__, type(arg).__name__)))
