Cannot get object from queryset

Code below should substitute all \[\[(.+)\]\] matches in 'content' field of AD with src of ADResource where (.+) is alias

[[Similac]] → media/banners/2011/07/24/ad1.gif

[[res]] → media/banners/2011/07/24/ad2.png

It catches DoesNotExist exception on [[res]] or [[Similac]] and returns 'res' or 'Similac' strings.

开发者_Go百科ADResource table contents:
id   alias      src 
----------------------------------------------------
1    Similac    media/banners/2011/07/24/ad1.gif
2    res        media/banners/2011/07/24/ad2.png


class ADResource(models.Model):
    alias = models.CharField(max_length=256)
    src = models.FileField(upload_to="media/banners/%Y/%m/%d/")  

class AD(models.Model):
    content = models.CharField(max_length=10000)

    def getResourceURL(object, object_alias):
        try:
            return ADResource.objects.all().get(alias="%s" % object_alias).src.url
        except ADResource.DoesNotExist:
            return object_alias

    def save(self, **kwargs):
        self.content = re.sub(r'\[\[(.+)\]\]', AD.getResourceURL(self, r'\1'), self.content)
        super(AD, self).save(**kwargs)

But this code is working and i get url of src field:

return ADResource.objects.all().get(alias='res').src.url

Oh, stupid question, i'm getting not a string but regex object and my match was in first subgroup.

self.content = re.sub(r'\[\[(.+)\]\]', lambda m: ADResource.objects.all().get(alias=m.group(1)).src.url, self.content)