python3中怎么判断传入的参数是否是unicode

Question

网上的教程都说使用isinstance( XXX , unicode)来判断
但是我在python3下这么使用会报name 'unicode' is not defined的错误，想看一下isinstance()是怎么实现的，传入参数的说明，结果发现isinstance的定义是下面这个样子，完全看不出想要判断unicode该传入什么参数，顺带问一下为什么python好多自带的参数都是这么定义的，def XXX(): return none，没有功能实现的代码

def isinstance(object, class_or_type_or_tuple):
  """ isinstance(object, class-or-type-or-tuple) -> bool
  
  Return whether an object is an instance of a class or of a subclass thereof.
  With a type as second argument, return whether that is the object's type.
  The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
  isinstance(x, A) or isinstance(x, B) or ... (etc.). """
  return None

回到正题，python3下该怎么判断是否unicode呢？

Answer 1

The basic str in Python 3 is unicode, so you can directly judge str:

>>> isinstance('s', str)
True

Answer 2

The bottom layer of cpython is implemented in C. The py source code of built-in functions and objects is just for decoration, just to provide you with some comments