<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def getPartitionList(self):
 """Returns list of partitions. @return: List of (disk,partition) pairs. """

        if self._partList is None:
            self._partList = []
            for (disk,parts) in self.getPartitionDict().iteritems():
                for part in parts:
                    self._partList.append((disk,part))
        return self._partList