old_contents: from comics.aggregator.crawler import CrawlerBase, CrawlerImage
  from comics.meta.base import MetaBase
  
  class Meta(MetaBase):
      name = 'Diesel Sweeties (web)'
      language = 'en'
      url = 'http://www.dieselsweeties.com/'
      start_date = '2000-01-01'
      rights = 'Richard Stevens'
  
  class Crawler(CrawlerBase):
      history_capable_date = '2000-01-01'
      schedule = 'Mo,Tu,We,Th,Fr'
      time_zone = -5
  
      def crawl(self, pub_date):
          feed = self.parse_feed('http://www.dieselsweeties.com/ds-unifeed.xml')
          for entry in feed.for_date(pub_date):
              if not entry.summary:
                  continue
              url = entry.summary.src('img[src*="/strips/"]')
              title = entry.title
              text = entry.summary.alt('img[src*="/strips/"]')
              return CrawlerImage(url, title, text)
  
new_contents: from comics.aggregator.crawler import CrawlerBase, CrawlerImage
  from comics.meta.base import MetaBase
  
  class Meta(MetaBase):
      name = 'Diesel Sweeties (web)'
      language = 'en'
      url = 'http://www.dieselsweeties.com/'
      start_date = '2000-01-01'
      rights = 'Richard Stevens'
  
  class Crawler(CrawlerBase):
      history_capable_date = '2000-01-01'
      schedule = 'Mo,Tu,We,Th,Fr'
      time_zone = -5
  
      def crawl(self, pub_date):
          feed = self.parse_feed('http://www.dieselsweeties.com/ds-unifeed.xml')
          for entry in feed.for_date(pub_date):
              if not hasattr(entry, 'summary'):
                  continue
              url = entry.summary.src('img[src*="/strips/"]')
              title = entry.title
              text = entry.summary.alt('img[src*="/strips/"]')
              return CrawlerImage(url, title, text)
  
subject: Check if field exists, not if it's empty