Modify Itertools.cycle()

Question

I'm currently using the itertools.cycle() object, and I was wondering if there was anyway to modify the cycle after it's creation. The following:

my_cycle = itertools.cycle([1,2,3])
print my_cycle.next()
my_cycle.delete()    #function doesn't exist
print my_cycle.next()

would have an output of:

1
3

Is there any way to achieve this through itertools? Or perhaps another object? Or do I need to implement my own object to do this.

Answer 1

Itertools doesn't provide such an option. You can build it with a deque:

from collections import deque

class ModifiableCycle(object):
    def __init__(self, items=()):
        self.deque = deque(items)
    def __iter__(self):
        return self
    def __next__(self):
        if not self.deque:
            raise StopIteration
        item = self.deque.popleft()
        self.deque.append(item)
        return item
    next = __next__
    def delete_next(self):
        self.deque.popleft()
    def delete_prev(self):
        # Deletes the item just returned.
        # I suspect this will be more useful than the other method.
        self.deque.pop()