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

[Lie Ryan]

Damon Timm wrote:
> Sorry for the double post!  Went off by mistake before I was done ...
> 
> Anyhow, I would like to have a tuple defined at the beginning of my
> code that includes classes *before* they are defined ... as such (this
> is on-the-fly-hack-code just for demonstrating my question):
> 

What you want to do can be done with a helper function (e.g. 
Sync.find_sync() below), but I smelled a bad class design. Anyway, here 
is how you would do it...

class Video(object):
     url = '...'
     def sync(self):
         sync = Sync.find_sync(self.url)

class Sync(object):
     class NoSuitableSync(Exception): pass

     @staticmethod
     def find_sync(url):
         for S in Sync.__subclasses__():
             if S.RE.match(url):
                 return S(url)
         raise Sync.NoSuitableSync()

class SyncYoutube(Sync):
     RE = re.compile(r'some regex here')
class SyncBlip(Sync):
     RE = re.compile(r'other regex here')


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.