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  1. class RpnException(Exception):
  2.     pass
  3.  
  4. def evalRPN(expr):
  5.     stack=[]
  6.     for a in expr.split():
  7.         if (a=='+'):
  8.             if (len(stack) < 2):
  9.         	    raise RpnException("Лишний знак +")
  10.             a2=stack[0]
  11.             a1=stack[1]
  12.             r=a1+a2
  13.             stack=[r]+stack[2:]
  14.         elif (a=='-'):
  15.             if (len(stack) < 2):
  16.         	    raise RpnException("Лишний знак -")
  17.             a2=stack[0]
  18.             a1=stack[1]
  19.             r=a1-a2
  20.             stack=[r]+stack[2:]
  21.         elif (a=='*'):
  22.             if (len(stack) < 2):
  23.         	    raise RpnException("Лишний знак *")
  24.             a2=stack[0]
  25.             a1=stack[1]
  26.             r=a1*a2
  27.             stack=[r]+stack[2:]
  28.         elif (a=='/'):
  29.             if (len(stack) < 2):
  30.         	    raise RpnException("Лишний знак /")
  31.             a2=stack[0]
  32.             a1=stack[1]
  33.             if (a2==0):
  34.                 raise RpnException("Деление на нуль!")
  35.             else:
  36.                 r=a1/a2
  37.             stack=[r]+stack[2:]
  38.         else:
  39.         	stack=[int(a)]+stack
  40.  
  41.     if (len(stack) != 1):
  42.         raise RpnException("Лишнее число")
  43.     return stack[0]
  44.  
  45. try:
  46.     print(evalRPN("12 3 + 5 /"))
  47. except RpnException as e:
  48.     print(e)
  49.  
  50.  
  51.  
Success #stdin #stdout 0.01s 27712KB
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3.0
https://ideone.com/C9Fdx3
language:
Python 3 (python  3.12)
created:
6 years ago
visibility:
public

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