Retrieves previously stored key from the storage

    :return value, stored in the storage

def get(self, key):
    """
    Retrieves previously stored key from the storage

    :return value, stored in the storage
    """
    if key not in self._keystore:
      return None

    rec = self._keystore[key]
    """:type rec InMemoryItemValue"""

    if rec.is_expired:
      self.delete(key)
      return None

    return rec.value