אתגרים בפייתון/מחשבון RPN פשוט

   1 """
   2 RPN calculator
   3 
   4 Enter numbers and operators separated by white space using RPN notation.
   5 
   6 Example:
   7     >>> 1 2 3 + -
   8     4.0
   9     
  10 By Nir Soffer <nirs at freeshell dot org>
  11 """
  12 
  13 # Strings to operations mapping
  14 import operator
  15 strToOperator = {
  16     '+': operator.add,
  17     '-': operator.sub,
  18     '*': operator.mul,
  19     '/': operator.div
  20     }
  21 
  22 def calc_rpn(rpn):
  23     rpn = rpn.split()
  24 
  25     # Get numbers
  26     numbers = []
  27     for item in rpn:
  28         if not item.isdigit():
  29             break
  30         numbers.append(float(item))
  31     #  And operators
  32     operators = [strToOperator[item] for item in rpn[len(numbers):]]
  33 
  34     # Calculate - pop the last two numbers, apply the operator
  35     # and append to numbers.
  36     for op in operators:
  37         numbers.append(op(numbers.pop(), numbers.pop()))
  38     return numbers[-1]
  39 
  40 
  41 while 1:
  42     rpn = raw_input("Enter RPN input: ")
  43     print calc_rpn(rpn)