Here is a very interesting function that let me solve this:
secondPart = s.parts[1]
for thisNote in s.parts[0].notes:
sys.stdout.write('at ' + str(thisNote.offset) + ' toppitch: ' + str(thisNote.ps))
soundingNotes = secondPart.getElementsByOffset(thisNote.offset, mustFinishInSpan=False, mustBeginInSpan=False)
try:
if soundingNotes > 0:
basslength = len(soundingNotes)
except:
basslength = 0
if basslength > 1:
print "oh ow, more then one note sounding in the bass."
if basslength > 0:
if soundingNotes[0].isRest:
sys.stdout.write(' bottompitch: R')
else:
sys.stdout.write(' bottompitch: ' + str(soundingNotes[0].ps)) # + ' from ' + str(soundingNotes[0].offset))
# print the previous note
soundingNotes2 = secondPart.getElementsByOffset(thisNote.offset-1, mustFinishInSpan=False, mustBeginInSpan=False)