class Calculation(object):
	"""a simple definition API"""
	def _make_ints(self, *args):
		try:
			return map(int, args)
		except ValueError:
			raise TypeError("Couldn't coerce arguments to integers: %s" % args)
	def add(self, a, b):
		a, b = self._make_ints(a, b)
		return a+b
	def subtract(self, a, b):
		a, b = self._make_ints(a, b)
		return a-b
	def multiply(self, a, b):
		a, b = self._make_ints(a, b)
		return a*b
	def divide(self, a, b):
		a, b = self._make_ints(a, b)
		return a/b