class MyTuple(tuple):
    def __init__ (self, values):
        self.xres = values[0]
        self.yres = values[1]
        tuple.__init__ (self, (self.xres, self.yres))

    def __str__ (self):
        return "%sx%s" % (self.xres, self.yres)

a = MyTuple((300, 300))
print a
print str (a)