You could just use a small memoize decorator like this one

  class Memoize:
	def __init__ (self, f):
		self.f = f
		self.mem = {}
	def __call__ (self, *args, **kwargs):
		if (args, str(kwargs)) in self.mem:
			return self.mem[args, str(kwargs)]
		else:
			tmp = self.f(*args, **kwargs)
			self.mem[args, str(kwargs)] = tmp
			return tmp