Simple iterator implementing a "back" method

gistfile1.py

class BackIterator(object):
    def __init__(self, iterator):
        self.current_index = 0
        self.max_index = 0
        self.previous_items = []
        self.iterator = iterator
 
    def __iter__(self):
        return self
 
    def __next__(self):
        if self.current_index == self.max_index:
            item = next(self.iterator)
            self.previous_items.append(item)
            self.max_index += 1
        else:
            item = self.previous_items[self.current_index]
        self.current_index += 1
        return item
   
    def __back__(self):
        if self.current_index < 1:
            raise IndexError("Already at beggining of the iterator")
        self.current_index -= 1
        return self.previous_items[self.current_index]
   
    # for style consistency and Python2 compatibility
    next = __next__
    back = __back__

Example usage:

>>> bla = Wrapper(open(<arquivo>))
>>> x  = iter(bla)
>>> x.next()
<linha1 do arquivo>
>>> x.next()
<linha2 do arquivo>
>>>x.back()
<linha2 do arquivo>