+ def assign_ids(self, existing=None):
+ # Find all existing IDs.
+ existing = existing or set()
+ que = [self.tree.getroot()]
+ while que:
+ item = que.pop(0)
+ try:
+ item.normalize_insides()
+ except AttributeError:
+ pass
+ existing.add(item.attrib.get('id'))
+ que.extend(item)
+
+ i = 1
+ que = [self.tree.getroot()]
+ while que:
+ item = que.pop(0)
+ que.extend(item)
+ if item.attrib.get('id'):
+ continue
+ if not getattr(item, 'SHOULD_HAVE_ID', False):
+ continue
+ while f'e{i}' in existing:
+ i += 1
+ item.attrib['id'] = f'e{i}'
+ i += 1
+