<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set(self, key, value, expire_in=None):
 """ Function to set or change particular property in the storage :param key: key name :param value: value to set :param expire_in: seconds to expire key :type key str :type expire_in int """

    if key not in self._keystore:
      self._keystore[key] = InMemoryItemValue(expire_in=expire_in)

    k = self._keystore[key]
    """:type k InMemoryItemValue"""
    k.update_expire_time(expire_in)
    k.value = value