引导我进行搜索的用例如下

def setfrom(self,f):
    """Set from iterable f"""
    fi = iter(f)
    for i in range(self.n):
        try:
            x = next(fi)
        except StopIteration:
            fi = iter(f)
            x = next(fi)
        self.a[i] = x 

hasnext()在哪里可用

def setfrom(self,f):
    """Set from iterable f"""
    fi = iter(f)
    for i in range(self.n):
        if not hasnext(fi):
            fi = iter(f) # restart
        self.a[i] = next(fi)

这对我来说更干净。显然，您可以通过定义实用程序类来解决这些问题，但接下来的情况是，您有20多种几乎等效的解决方法，每种方法都有各自的怪癖，如果您希望重用使用不同解决方法的代码，那么您必须在单个应用程序中有多个几乎等效的代码，或者四处挑选并重写代码以使用相同的方法。“只做一次，就把它做好”的格言很失败。

此外，迭代器本身需要有一个内部的“hasnext”检查，以查看是否需要引发异常。然后，这个内部检查被隐藏起来，因此需要通过尝试获取一个项、捕捉异常并在抛出异常时运行处理程序来测试它。在我看来，这是不必要的隐藏。

也许只有我这么想，但虽然我喜欢https://stackoverflow.com/users/95810/alex-martelli的答案，但我发现这个更容易读:

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

class MyIterator(Iterator):  # need to subclass Iterator rather than object
  def __init__(self, it):
    self._iter = iter(it)
    self._sentinel = object()
    self._next = next(self._iter, self._sentinel)
    
  def __iter__(self): 
    return self
  
  def __next__(self):        # __next__ vs next in python 2
    if not self.has_next():
      next(self._iter)  # raises StopIteration

    val = self._next
    self._next = next(self._iter, self._sentinel)
    return val
  
  def has_next(self):
    return self._next is not self._sentinel

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

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

你可以使用itertools来tee迭代器。在teed迭代器上检查StopIteration。