itertools.groupby() not grouping correctly
itertools.groupby collects together contiguous items with the same key.
If you want all items with the same key, you have to sort self.data first.
for mid, group in itertools.groupby(
sorted(self.data,key=operator.itemgetter(1)), key=operator.itemgetter(1)):
Variant without sorting (via dictionary). Should be better performance-wise.
def full_group_by(l, key=lambda x: x):
d = defaultdict(list)
for item in l:
d[key(item)].append(item)
return d.items()