[Tutor] Store Class in Tuple Before Defining it ...

[Damon Timm]

Hi Everyone - thanks for your responses.  Answered my direct questions:

[1] can't be done at the top and
[2] would have to move the tuple somewhere else

as well as gave me some new ideas about completely rethinking the
design ... I love keeping the RE definitions with the child classes
... makes it easy just to add a child anywhere without having to fool
with the original code.

One of my issues has been fixed using the @staticmethod decorator
(which I did not know about).  Here is what I have now, and my final
question (perhaps) follows.

####
#this is a django app, by the way

class Video(models.Model):
    url             = models.URLField('Video URL')
    # more fields and functions here

    def sync(self):
        'Update videos external data - for children only'
        pass

    @staticmethod
    def add_video(url):
        'add a video only if it matches correct regex -- need ExceptionHandler'
        for sc in Video.__subclasses__():
            if sc.RE.match(url):
                return sc(url=url)

class YoutubeVideo(Video):
    RE = re.compile(r'([^(]|^)http://www\.youtube\.com/watch\?\S*v=(?P<youtubeid>[A-Za-z0-9_-]+)\S*')

    def sync(self):
        # do custom syncing here
        print "am syncing a YOUTUBE video"

class ViemoVideo(Video):
    RE = re.compile(r'([^(]|^)http://(www.|)vimeo\.com/(?P<vimeoid>\d+)\S*')

    def sync(self):
        # do custom syncing here
        print "am syncing a VIMEO video"
##############

So, this is *great* because now I can "add_video" without knowing the
video url type at all.

>>> v = Video.add_video(url="http://www.youtube.com/watch?v=UtEg3EQwN9A")
>>> v
<YoutubeVideo: >
>>>

Perfect!  The last part is figuring out the syncing -- what I would
like to do would be either:

>>> Video.sync_all_videos() #create another static method

Or, if I had to, create another function that did a:

>>> for video in Video.objects.all(): # object.all() is a django function that returns everything
...         video.sync()

However, I am not sure how to determine the "actual" class of a video
when I am dealing only with the parent.  That is, how do I call a
child's sync() function when I am dealing the parent object?  As
suggested (in email below) I could re-run the regex for each parent
video for each sync, but that seems like it could be an expensive
operation (supposing one day I had thousands of videos to deal with).

Is there another easy way to find the "real" class of an object when
dealing with the parent?  I know so little, I have to think there
might be something (like the @staticmethod decorator!).

Thanks again!

Damon


On Sat, Aug 29, 2009 at 8:05 AM, Lie Ryan<lie.1296 at gmail.com> wrote:
> what I suggest you could do:
>
> class Video(object):
>    # Video is a mixin class
>    def __init__(self, url):
>        self.url = url
>    def sync(self):
>        # source agnostic sync-ing or just undefined
>        pass
>    @staticmethod
>    def find_video(url):
>        for sc in Video.__subclasses__():
>            if sc.RE.match(url)
>                return sc(url)
> class Youtube(Video):
>    RE = re.compile('... some regex here ...')
>    def sync(self):
>        # costum sync-ing
>        pass
> class Blip(Video):
>    RE = re.compile('... other regex here ...')
>    def sync(self):
>        # costum sync-ing
>        pass
> a = Video.find_video('http://www.youtube.com/xxxx')
>
> that way, url detection will only happen on class initialization instead of
> every time sync is called.