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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def s(self):
 		""" 		step to the next node in the execution order 		"""

		next_node=self._exe_order[self.step]
		self._eval(next_node)
		self.step+=1
		if self.step==len(self._exe_order):
			return self._finish()
		else:
			# if stepping, return the value of the node we just
			# evaled
			return self._break(value=self._cache.get(next_node.name))