<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def delLadder(name):
 """forget about a previously defined Ladder setting by deleting its disk file"""

    ladders = getKnownLadders()
    try:
        ladder = ladders[name]
        os.remove(ladder.filename) # delete from disk
        del ladders[name] # deallocate object
        return ladder
    except KeyError:
        raise ValueError("given ladder name '%s' is not a known ladder definition"%(name))