f = file(fn)
        data = dict.fromkeys(data_keys, None)
        boundaries = []
        # read boundaries
        while True:
            line = f.readline()
            boundaries.append(int(line.strip()))
            if not line or len(boundaries) == len(data_keys):    
                break
        # read data
        for idx, data_length in enumerate(boundaries):
            key = data_keys[idx]
            tmp = f.read(data_length)
            data[key] = tmp
        f.close()