[Tutor] PolyRange -- iterator

[Stefan Lesicnik]

On Wed, Nov 4, 2009 at 7:17 PM, Hugo Arts <hugo.yoshi at gmail.com> wrote:
> On Wed, Nov 4, 2009 at 5:38 PM, spir <denis.spir at free.fr> wrote:
>> Hello,
>>
>> as I was crawling in endless complications with unadequate ranges, I decided to create a "PolyRange" type able to hold arbitrary many "sub-range"; which means finally a big range with wholes in it. This whole stuff again to cope with unicode -- a poly-range would be able to hold a range for a char class (eg 'letter') which spans over several ordinal ranges. (Viva unicode consortium!)
>>
>> So, it works as needed. It is even able to "stretch" over addictional sub-ranges or to "unite" with a poly-range brother (sister, too). See code below.
>>
>> Now, I need it to be properly iterable if needed -- the main use beeing indeed the 'in' operator -- but who knows. So, I tried to implement __iter__ and next (by the way, why isin't it called __next__ instead, looks strange for a python builtin?). Seems to work, but the result looks veeery heavy to my eyes. As I had never written an iterator before, would be nice and criticize the code?
>>
>
> You're right, next() should really be called __next__(), and this is
> actually fixed in python 3 (don't know why it wasn't originally done
> this way).
>
> Now, the code. If you write __iter__ as a generator, you won't have to
> write a next method at all. It simplifies The thing a whole lot:
>
> def __iter__(self):
>    for range in self.ranges:
>        for item in range:
>            yield item
>
> That's it. Alternatively, you could turn the whole thing into a
> one-liner and just return a generator expression from __iter__:
>
> def __iter__(self):
>    return (item for r in self.ranges for item in r)
>
> It's not as clear though, and it doesn't save that much space. I like
> the first one slightly better.
>
> python documentation on generators:
> http://docs.python.org/tutorial/classes.html#generators

I dont know much about generators, but this link was posted earlier
this week and i learnt alot from it (actually some basics, like what
happens when you iterate over different objects!)

http://www.dabeaz.com/generators-uk/

(its the PDF presentation)

Stefan