class Value:
	def __init__(self, initial=None):
		self.value = initial
		self.has_changed = True

	def set(self, value):
		self.has_changed = self.value != value
		self.value = value

	def is_changed(self):
		return self.has_changed

	def get(self):
		self.has_changed = False
		return self.value


class ValueChanged(object):
	def __init__(self, on_changed, prec=2, initial=None):
		self.on_changed = on_changed
		self.prec = prec
		self.value = initial

	def set(self, value):
		has_changed = True
		value_rounded = round(value, self.prec)
		if self.value is not None:
			has_changed = self.value != value_rounded

		self.value = value_rounded
		if has_changed:
			self.on_changed(value_rounded)