what's the problem with the code:
self.x = x
self.y = y
self.z = z;
return '"' + str("(%s,%s,%)"%(self.x,self.y,self.z)) + '"'
my_point = Point3D(1,2,3)
output : "(1,2,3)"
its giving me the error as it looks like you didn't print "(1,2,3)"