Extract a list from itertools.cycle

user_741316 0
Viewed 3091

I have a class which contains a itertools.cycle instance which I would like to be able to copy. One approach (the only one I can come up with), is to extract the initial iterable (which was a list), and store the position that the cycle is at.

Unfortunately I am unable to get hold of the list which I used to create the cycle instance, nor does there seem to be an obvious way to do it:

import itertools
c = itertools.cycle([1, 2, 3])
print dir(c)
['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', 
 '__hash__', '__init__', '__iter__', '__new__', '__reduce__', 
 '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', 
 '__subclasshook__', 'next']

I can come up with some half reasonable reasons why this would be disallowed for some types of input iterables, but for a tuple or perhaps even a list (mutability might be a problem there), I can't see why it wouldn't be possible.

Anyone know if its possible to extract the non-infinite iterable out of an itertools.cycle instance. If not, anybody know why this idea is a bad one?

itertools python-2.7 python
4 Answers

Depending on how you're using cycle, you could even get away with a custom class wrapper as simple as this:

class SmartCycle:
    def __init__(self, x):
        self.cycle = cycle(x)
        self.to_list = x

    def __next__(self):
        return next(self.cycle)

e.g.

> a = SmartCycle([1, 2, 3])
> for _ in range(4):
>     print(next(a))
1
2
3
1

> a.to_list
[1, 2, 3]
user_35118190
Related