is_pseq(arg) yields True if arg is a persistent vector, a persistent list, a tuple, or a numpy
      array with its writeable flag off.

def is_pseq(arg):
    '''
    is_pseq(arg) yields True if arg is a persistent vector, a persistent list, a tuple, or a numpy
      array with its writeable flag off.
    '''
    if is_nparray(arg): return arg.flags['WRITEABLE'] == False
    return isinstance(arg, (tuple_type, pyr.PVector, pyr.PList))