What's the Pythonic way to do this?

[Doug Rosser]

class Cycle(object):

def __init__(self, inputList):
object.__init__ (self)
self.index = 0
self.limit = len(inputList)
self.list = inputList

def next(self):
"""
returns the next element of self.list, jumping
back to the head of the list if needed.
Yes, this is an infinite loop. (Use with caution)
Arguments:
none
Returns:
the next element of self.list
"""
if self.index+1 < self.limit:
self.index+=1
return self.list[self.index-1]
else:
self.index=0
return self.list[self.limit-1]

[Steven Bethard]

Re: What's the Pythonic way to do this?

Doug Rosser <da_rosser <at> yahoo.com> writes:[color=blue]
>
> class Cycle(object):
>
> def __init__(self, inputList):
> object.__init__ (self)
> self.index = 0
> self.limit = len(inputList)
> self.list = inputList
>
> def next(self):
> """
> returns the next element of self.list, jumping
> back to the head of the list if needed.
> Yes, this is an infinite loop. (Use with caution)
> Arguments:
> none
> Returns:
> the next element of self.list
> """
> if self.index+1 < self.limit:
> self.index+=1
> return self.list[self.index-1]
> else:
> self.index=0
> return self.list[self.limit-1][/color]

Well, if all you want to do is cycle through the elements of a list, I'd
suggest:
[color=blue][color=green][color=darkred]
>>> import itertools
>>> itertools.cycle (inputList)[/color][/color][/color]

If you're really asking about how to write the class, I might write it like:
[color=blue][color=green][color=darkred]
>>> class Cycle(object):[/color][/color][/color]
.... def __init__(self, lst):
.... self.index = -1
.... self.list = lst
.... def next(self):
.... self.index = (self.index + 1) % len(self.list)
.... return self.list[self.index]

Steve

[Peter Hansen]

Re: What's the Pythonic way to do this?

Doug Rosser wrote:[color=blue]
> class Cycle(object):
>
> def __init__(self, inputList):
> object.__init__ (self)
> self.index = 0
> self.limit = len(inputList)
> self.list = inputList
>
> def next(self):
> """
> returns the next element of self.list, jumping
> back to the head of the list if needed.
> Yes, this is an infinite loop. (Use with caution)
> Arguments:
> none
> Returns:
> the next element of self.list
> """
> if self.index+1 < self.limit:
> self.index+=1
> return self.list[self.index-1]
> else:
> self.index=0
> return self.list[self.limit-1][/color]

I think this is spelled like this now:

import itertools
mycycle = itertools.cycle (inputList)

-Peter

[Aahz]

Re: What's the Pythonic way to do this?

In article <qcOdnYlYFO0Wjt _cRVn-tQ@powergate.ca >,
Peter Hansen <peter@engcorp. com> wrote:[color=blue]
>Doug Rosser wrote:[color=green]
>> class Cycle(object):
>>
>> def __init__(self, inputList):
>> object.__init__ (self)
>> self.index = 0
>> self.limit = len(inputList)
>> self.list = inputList
>>
>> def next(self):
>> """
>> returns the next element of self.list, jumping
>> back to the head of the list if needed.
>> Yes, this is an infinite loop. (Use with caution)
>> Arguments:
>> none
>> Returns:
>> the next element of self.list
>> """
>> if self.index+1 < self.limit:
>> self.index+=1
>> return self.list[self.index-1]
>> else:
>> self.index=0
>> return self.list[self.limit-1][/color]
>
>I think this is spelled like this now:
>
>import itertools
>mycycle = itertools.cycle (inputList)[/color]

That doesn't appear to work if self.list gets mutated. Then again, the
OP's version doesn't work, either. I'd use a linked list myself.
--
Aahz (aahz@pythoncra ft.com) <*> http://www.pythoncraft.com/

"A foolish consistency is the hobgoblin of little minds, adored by little
statesmen and philosophers and divines." --Ralph Waldo Emerson

[Phillip J. Eby]

Re: What's the Pythonic way to do this?

da_rosser@yahoo .com (Doug Rosser) wrote in message news:<e08cd05f. 0409101235.50b1 f8f3@posting.go ogle.com>...[color=blue]
> class Cycle(object):
> [snip][/color]

def cycle(inputList ):
while True:
for item in inputList:
yield item

Or, as others have pointed out, there's an itertools.cycle that does
the same thing, at least in Python 2.3 and up.