PredictableIterator.py

class PredictableIterator(object):
  def __init__(self, iterator):
    self.iterator = iter(iterator)
    self._next = None

  def __iter__(self): return self

  def next(self):
    if self._next:
      result = self._next
    else:
      result = next(self.iterator)
    self._next = None
    return result

  def has_next(self):
    if self._next is None:
      try: self._next = next(self.iterator)
      except StopIteration: self._next = False
      else: self._next = True
    return self._next