':param policy: an instance of ECStoragePolicy
:param timestamp_str: a string representation of a timestamp'

def __init__(self, policy, timestamp_str):

    self.policy = policy
    self.timestamp_str = timestamp_str
    self.gets = collections.defaultdict(list)
    self.alt_nodes = collections.defaultdict(list)
    self._durable = False
    self.status = self.headers = None
