from itertools import groupby

log = [
  {"time": 201201, "x": 2},
  {"time": 201201, "y": 7},
  {"time": 201201, "z": 2},
  {"time": 201202, "a": 3},
  {"time": 201202, "b": 4},
  {"time": 201202, "c": 0}
]



def transmogify(data):
    res = []
    for k, g in groupby(data, lambda d: d['time']):
        d = {'time': k}
        for dic in g:
            d.update(dic)
        res.append(d)
    return res

print(transmogify(log))

# [{'y': 7, 'x': 2, 'z': 2, 'time': 201201}, {'a': 3, 'c': 0, 'b': 4, 'time': 201202}]