':returns: List of trackers, supports single-tracker and multi-tracker implementations'

@property
def trackers(self):

    trackers = []
    for tl in self.content.get(u'announce-list', []):
        for t in tl:
            trackers.append(t)
    if (not (self.content.get(u'announce') in trackers)):
        trackers.append(self.content.get(u'announce'))
    return trackers
