cyclic iterators ?

[Tool69]

Hi,

Let say I've got a simple list like my_list = [ 'a', ',b', 'c' ].
We can have an iterator from it by k = iter( my_list), then we can
access each of her (his ?) element by k.next(), etc.

Now, I just wanted k to have the following cyclic behaviour (without
rising the ) :

>k.next()

'a'

>k.next()

'b'

>k.next()

'c'

>k.next() -not raising StopIteration error

'a'

>k.next()

'b'
etc.

I've tried something like this to have a cyclic iterator without
sucess:

def iterate_mylist(my_list):
k = len((my_list)
i=0
while i <= k :
yield my_list[i]
i += 1
i = 0
yield my_list[0]

I missed something, but I don't know what exactly.
Thanks.

[Bruno Desthuilliers]

Tool69 a écrit :

Hi,

Let say I've got a simple list like my_list = [ 'a', ',b', 'c' ].
We can have an iterator from it by k = iter( my_list), then we can
access each of her (his ?) element by k.next(), etc.

Now, I just wanted k to have the following cyclic behaviour (without
rising the ) :

>>>k.next()

'a'

>>>k.next()

'b'

>>>k.next()

'c'

>>>k.next() -not raising StopIteration error

'a'

>>>k.next()

'b'
etc.

I've tried something like this to have a cyclic iterator without
sucess:

(snip code)

I missed something, but I don't know what exactly.

from itertools import cycle

HTH

[Paul Rubin]

"Tool69" <ki****************@gmail.comwrites:

I've tried something like this to have a cyclic iterator without
sucess:

def iterate_mylist(my_list):
k = len((my_list)
i=0
while i <= k :
yield my_list[i]
i += 1
i = 0
yield my_list[0]

I missed something, but I don't know what exactly.

As Bruno says, you can use itertools.cycle, but the problem above is
that you're not looping repeatedly through the list; you yield all the
elements, then yield the first element again, then stop. So for
['a','b','c'] you'd yield the sequence a,b,c,a.

I'd rewrite the above something like:

def iterate_mylist(my_list):
while True:
for m in my_list:
yield m

This just loops through the list over and over again.

[tool69]

Paul Rubin a écrit :

>
As Bruno says, you can use itertools.cycle, but the problem above is
that you're not looping repeatedly through the list; you yield all the
elements, then yield the first element again, then stop. So for
['a','b','c'] you'd yield the sequence a,b,c,a.

Yes, that was the problem.
Thanks for the explanation and for the cycle() function from itertool
that I missed.

[MRAB]

On Mar 3, 1:27 am, Paul Rubin <http://[e-mail]:

"Tool69" <[e-mail]:

I've tried something like this to have a cyclic iterator without
sucess:

def iterate_mylist(my_list):
k = len((my_list)
i=0
while i <= k :
yield my_list[i]
i += 1
i = 0
yield my_list[0]

I missed something, but I don't know what exactly.

As Bruno says, you can use itertools.cycle, but the problem above is
that you're not looping repeatedly through the list; you yield all the
elements, then yield the first element again, then stop. So for
['a','b','c'] you'd yield the sequence a,b,c,a.

I'd rewrite the above something like:

def iterate_mylist(my_list):
while True:
for m in my_list:
yield m

This just loops through the list over and over again.

Another problem is that it should be i < k, not i <= k.