Question

I’m trying to write a class which works in the same way as the cycle from itertools module but has some additional functionality. I want to have possibility to remove elements from a list along which I’m iterating.

Here is my code:

class myCycle(object):
    def __init__(self, list):
        self.list = list

    def __iter__(self):
        def iter(self):
            while True:
                if not self.list:
                    break
                for e in self.list:
                    yield e
        return iter(self)

    def remove(self, e):
        self.list.remove(e)

It works fine with one exception. Let’s look at example:

>>> for i in c:
...     print i
...     if i == 1:
...         c.remove(1)
...     if i == 3:
...         break
... 
1
3
>>> 

After removing 1 from the list, index move and that is probably reason why I don’t have 2 in my output.

But how can I get it working? Or maybe there is some other way to get this functionality?

EDIT:

After your comments I will try to explain what I’m trying to do.

I have a string with player actions which can look like this one:

actions = "sBcffcffcfrfccc"

It’s from poker, action f mean fold, c call and so one. Most interesting for us is fold.

And I also have list of players:

players = ['Saxum', 'Erasmus', 'Anders', 'Ginger', 'Adam',
           'Crusoe', 'OgoPogo', 'Hari', 'Sanja', 'Hooke']

And I want to assign action to each player. So we are going through actions and players:

Saxum -> s
Erasmus -> B
Anders -> c
Ginger -> f

Ginger folded, we should remove this player. So how player list look like now:

    players = ['Saxum', 'Erasmus', 'Anders', 'Adam',
               'Crusoe', 'OgoPogo', 'Hari', 'Sanja', 'Hooke']

Adam -> f

Adam folded, we should remove this player. So how player list look like now:

    players = ['Saxum', 'Erasmus', 'Anders', 
               'Crusoe', 'OgoPogo', 'Hari', 'Sanja', 'Hooke']

Crusoe -> c
OgoPogo -> f

OgoPogo folded, we should remove this player. So how player list look like now:

    players = ['Saxum', 'Erasmus', 'Anders', 
               'Crusoe', 'Hari', 'Sanja', 'Hooke']

Hari -> f

Hari folded, we should remove this player. So how player list look like now:

    players = ['Saxum', 'Erasmus', 'Anders', 
               'Crusoe', 'Sanja', 'Hooke']

Sanja -> c
Hooke -> f

Hooke folded, we should remove this player. So how player list look like now:

    players = ['Saxum', 'Erasmus', 'Anders', 
               'Crusoe', 'Sanja']

Hooke was last on the list, so we start from beginning.

Saxum -> r
Erasmus -> f

Erasmus folded, we should remove this player. So how player list look like now:

    players = ['Saxum', 'Anders', 
           'Crusoe', 'Sanja']

Anders -> c
Crusoe -> c
Sanja -> c

And that was reason why I started to implement myCycle. But maybe there is better way to do this?

Answer 1

Don’t remove the items that are gone from the list — replace them with None instead:

class MyCycle(object):
    def __init__(self, lst):
        self.list = lst

    def __iter__(self):
        while True:
            items_left = False
            for x in self.list:
                if x is not None:
                    items_left = True
                    yield x
            if not items_left:
                return

    def remove(self, e):
        self.list[self.list.index(e)] = None