What are the differences between the following two implementations of singleton design pattern in Python?

What are the differences between the following two implementations of singleton design pattern in Python?

What are the differences between their intended usages?

---

From Python in a Nutshell

class Singleton(object):
    _singletons = {}
    def __new__(cls, *args, **kwds):
        if cls not in cls._singletons:
            cls._singletons[cls] = super(Singleton, cls).__new__(cls)
        return cls._singletons[cls]

any subclass of Singleton (that does not further override __new__ ) has exactly one instance.

---

From Usage of super in singleton

class Singleton(object):
  def __new__(cls, *args, **kw):
      if not hasattr(cls, '_instance'):
        orig = super(Singleton, cls)
        cls._instance = orig.__new__(cls, *args, **kw)
      return cls._instance