也可以实现一个helper生成器，它包装任何迭代器，并回答问题，如果它有next值:

在网上试试!

def has_next(it):
    first = True
    for e in it:
        if not first:
            yield True, prev
        else:
            first = False
        prev = e
    if not first:
        yield False, prev

for has_next_, e in has_next(range(4)):
    print(has_next_, e)

输出:

True 0
True 1
True 2
False 3

该方法的主要缺点(可能也是唯一的缺点)是它会多预读一个元素，对于大多数任务来说，它是完全可以的，但对于某些任务，它可能是不允许的，特别是如果has_next()的用户没有意识到这种预读逻辑，可能会误用它。

上面的代码也适用于无限迭代器。

实际上，对于所有的情况下，我曾经编写这样的has_next()是完全足够的，没有造成任何问题，事实上是非常有用的。你只需要知道它的预读逻辑。

使用“for”可以实现他自己版本的“next”避免异常

def my_next(it):
    for x in it:
        return x
    return None

为了读取所有迭代，基于处理“StopIteration”执行的解决方法非常简单:

    end_cursor = False
    while not end_cursor:
        try:
            print(cursor.next())
        except StopIteration:
            print('end loop')
            end_cursor = True
        except:
            print('other exceptions to manage')
            end_cursor = True

如果您确实需要一个has-next功能，那么使用一个小包装器类很容易获得它。例如:

class hn_wrapper(object):
  def __init__(self, it):
    self.it = iter(it)
    self._hasnext = None
  def __iter__(self): return self
  def next(self):
    if self._hasnext:
      result = self._thenext
    else:
      result = next(self.it)
    self._hasnext = None
    return result
  def hasnext(self):
    if self._hasnext is None:
      try: self._thenext = next(self.it)
      except StopIteration: self._hasnext = False
      else: self._hasnext = True
    return self._hasnext

现在就像

x = hn_wrapper('ciao')
while x.hasnext(): print next(x)

发出

c
i
a
o

是必需的。

Note that the use of next(sel.it) as a built-in requires Python 2.6 or better; if you're using an older version of Python, use self.it.next() instead (and similarly for next(x) in the example usage). [[You might reasonably think this note is redundant, since Python 2.6 has been around for over a year now -- but more often than not when I use Python 2.6 features in a response, some commenter or other feels duty-bound to point out that they are 2.6 features, thus I'm trying to forestall such comments for once;-)]]

===

对于Python3，您将进行以下更改:

from collections.abc import Iterator  # since python 3.3 Iterator is here

class hn_wrapper(Iterator):  # need to subclass Iterator rather than object
  def __init__(self, it):
    self.it = iter(it)
    self._hasnext = None
    
  def __iter__(self): 
    return self
  
  def __next__(self):        # __next__ vs next in python 2
    if self._hasnext:
      result = self._thenext
    else:
      result = next(self.it)
    self._hasnext = None
    return result
  
  def hasnext(self):
    if self._hasnext is None:
      try: 
        self._thenext = next(self.it)
      except StopIteration: 
        self._hasnext = False
      else: self._hasnext = True
    return self._hasnext

除了所有提到的StopIteration, Python的“for”循环只是做你想要的:

>>> it = iter("hello")
>>> for i in it:
...     print i
...
h
e
l
l
o

hasNext在某种程度上转换为StopIteration异常，例如:

>>> it = iter("hello")
>>> it.next()
'h'
>>> it.next()
'e'
>>> it.next()
'l'
>>> it.next()
'l'
>>> it.next()
'o'
>>> it.next()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

StopIteration文档:http://docs.python.org/library/exceptions.html#exceptions.StopIteration 一些关于python中的迭代器和生成器的文章:http://www.ibm.com/developerworks/library/l-pycon.html