<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def processing_block_list():
 """Return the list of processing blocks known to SDP."""

    pb_list = ProcessingBlockList()
    return dict(active=pb_list.active,
                completed=pb_list.completed,
                aborted=pb_list.aborted)