Given a dictionary list, creates a new list with grouped dictionaries based on a single key (label) and summing the value of other dictionary fields as convenient

dict_group.py

import itertools

item_list = [
    {'counter1': 1, 'label': '20150408154801', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154801', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154801', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154819', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154819', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154819', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154819', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154841', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154841', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154841', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408154841', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408155336', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408155336', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408155336', 'counter2': 0, 'counter3': 0},
    {'counter1': 1, 'label': '20150408155336', 'counter2': 0, 'counter3': 0},
    {'counter1': 0, 'label': '20150408155336', 'counter2': 1, 'counter3': 0},
    {'counter1': 0, 'label': '20150408155336', 'counter2': 1, 'counter3': 0},
    {'counter1': 0, 'label': '20150408155336', 'counter2': 0, 'counter3': 1},
    {'counter1': 0, 'label': '20150408155336', 'counter2': 0, 'counter3': 1},
    {'counter1': 0, 'label': '20150408155336', 'counter2': 1, 'counter3': 0},
    {'counter1': 0, 'label': '20150408155336', 'counter2': 1, 'counter3': 0}]
grouped_dicts = []
summable = ['counter1', 'counter2', 'counter3']
for s in summable:
    for key, group in itertools.groupby(item_list, lambda d: d['label']):
        d[s] = sum([d[s] for d in group])
        if d not in grouped_dicts:
            grouped_dicts.append(d)
print grouped_dicts