[Python-Dev] Proposal: new list function: pack

[Isaac Morland]

On Fri, 20 Mar 2009, paul bedaride wrote:

> I propose a new function for list for pack values of a list and
> sliding over them:
>
> then we can do things like this:
> for i, j, k in pack(range(10), 3, partialend=False):
>    print i, j, k
>
> I propose this because i need a lot of times pack and slide function
> over list and this one
> combine the two in a generator way.

See the Python documentation for zip():

http://docs.python.org/library/functions.html#zip

And this article in which somebody independently rediscovers the idea:

http://drj11.wordpress.com/2009/01/28/my-python-dream-about-groups/

Summary: except for the "partialend" parameter, this can already be done 
in a single line.  It is not for me to say whether this nevertheless would 
be useful as a library routine (if only perhaps to make it easy to specify 
"partialend" explicitly).

It seems to me that sometimes one would want izip instead of zip.  And I 
think you could get the effect of partialend=True in 2.6 by using 
izip_longest (except with an iterator result rather than a list).

> def pack(l, size=2, slide=2, partialend=True):
>    lenght = len(l)
>    for p in range(0,lenght-size,slide):
>        def packet():
>            for i in range(size):
>                yield l[p+i]
>        yield packet()
>    p = p + slide
>    if partialend or lenght-p == size:
>        def packet():
>            for i in range(lenght-p):
>                yield l[p+i]
>        yield packet()

Isaac Morland			CSCF Web Guru
DC 2554C, x36650		WWW Software Specialist