Also, your compare function is incorrect. It needs to return -1, 0, or 1, not a boolean as you have it. The correct compare function would be:
def compare(item1, item2):
if fitness(item1) < fitness(item2):
return -1
elif fitness(item1) > fitness(item2):
return 1
else:
return 0
# Calling
list.sort(key=compare)