code: def get(self, key):
      
      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
docs: Retrieves previously stored key from the storage
  
      :return value, stored in the storage