Daily Programmer #206 naive implementation

recurrence_hard.py

#!/usr/bin/python

func_dict = {
	'+' : lambda x,y:y+x,
	'-' : lambda x,y:y-x,
	'*' : lambda x,y:y*x,
	'/' : lambda x,y:y/x
}
# Given the RPN string, return a function that calculates the nth term
# based on the list of previous terms.
def create_func_naive(data):
	def recurse(n, acc):
		stack = []
		for atom in data.split():
			# XXX - probably don't need to check both paren's
			if '(' in atom and ')' in atom:
				index = n-int(atom[1:-1])
				if index < 0: return None
				term = acc[index]
				# Reference undefined term
				if term == None: return None
				stack.append(term)
			# lol
			elif atom in '+-*/':
				stack.append(func_dict[atom](stack.pop(), stack.pop()))
			else: stack.append(int(atom))
		return stack[0]
	return recurse

data = {}
func = create_func_naive(input())
nums = list(map(int, input().split(':')))
while len(nums) == 2:
	data[nums[0]] = nums[1]
	nums = list(map(int, input().split(':')))
top = nums[0]+1
for i in range(top):
	if i not in data: data[i] = func(i, data)
for i in data:
	if data[i] is not None: print('%s:\t%s' % (i, data[i]))
input()