Question

Python 2.6+ and 3.* have next(), but pre-2.6 only offers the object.next method. Is there a way to get the next() style in pre-2.6; some “def next():” construction perhaps?

Answer 1

class Throw(object): pass
throw = Throw() # easy sentinel hack
def next(iterator, default=throw):
  """next(iterator[, default])

  Return the next item from the iterator. If default is given
  and the iterator is exhausted, it is returned instead of
  raising StopIteration.
  """
  try:
    iternext = iterator.next.__call__
    # this way an AttributeError while executing next() isn't hidden
    # (2.6 does this too)
  except AttributeError:
    raise TypeError("%s object is not an iterator" % type(iterator).__name__)
  try:
    return iternext()
  except StopIteration:
    if default is throw:
      raise
    return default

(throw = object() works too, but this generates better docs when inspecting, e.g. help(next). None is not suitable, because you must treat next(it) and next(it, None) differently.)