Python-based Reverse Polish computing expressions

This article mainly introduces python's method for implementing the inverse Polish expression, and analyzes in detail the concept and implementation skills of the inverse Polish expression, which has some reference value, for more information about how to implement the inverse Polish expression in python, see the example in this article. Share it with you for your reference. The specific analysis is as follows:

A reverse Polish expression is also called a suffix expression. In a common expression, binary operators are always placed between two related computing objects. Therefore, this representation is also called an infix representation. J. Lukasiewicz, a Polish Logologist, proposed another expression method in 1929. In this method, each operator is placed after its operation object, so it is called a suffix.

# -*- coding: utf-8 -*-symbol_priority = {}symbol_priority[0] = ['#']symbol_priority[1] = ['(']symbol_priority[2] = ['+', '-']symbol_priority[3] = ['*', '/']symbol_priority[4] = [')']def comparePriority(symbol, RPN_stack, symbol_stack):  '''Compare priority between two symbols'''  global symbol_priority  if len(symbol_stack) > 0:    symbol_pop = symbol_stack.pop()  else:    return  for list in symbol_priority.values():    if (symbol in list) and (symbol_pop in list):      '''same priority'''      symbol_stack.append(symbol_pop)      symbol_stack.append(symbol)      return    elif symbol in list:      '''symbol is smaller'''      RPN_stack.append(symbol_pop)      #recusion call      comparePriority(symbol, RPN_stack, symbol_stack)      return    elif symbol_pop in list:      '''symbol is bigger'''      symbol_stack.append(symbol_pop)      symbol_stack.append(symbol)      return    else:      continue    symbol_stack.append(symbol_pop)    returndef scanEveryone(input_string, RPN_stack, symbol_stack):  for ch in input_string:    if ch.isdigit():      RPN_stack.append(ch)    else:      if len(symbol_stack) > 0:        if ch == '(':          symbol_stack.append(ch)        elif ch == ')':          while True:            symbol_pop = symbol_stack.pop()            if symbol_pop == '(':              break            else:              RPN_stack.append(symbol_pop)        else:          comparePriority(ch, RPN_stack, symbol_stack)      else:        symbol_stack.append(ch)def scanInput(RPN_stack, symbol_stack):  input_string = raw_input()  input_string += '#'  scanEveryone(input_string, RPN_stack, symbol_stack)def calRPN(RPN_stack):  value_stack = []  RPN_stack.append('#')  for value in RPN_stack:    if value == '#':      return value_stack.pop()      break    if value.isdigit():      value_stack.append(value)    else:      right_value = value_stack.pop()      left_value = value_stack.pop()      cal_string = left_value + value + right_value      value_stack.append(str(eval(cal_string)))def main():  RPN_stack = []  symbol_stack = []  scanInput(RPN_stack, symbol_stack)  print calRPN(RPN_stack)if __name__ == '__main__':  main()

CalRPN. py

# -*- coding: utf-8 -*-symbol_priority = {}symbol_priority[0] = ['#']symbol_priority[1] = ['(']symbol_priority[2] = ['+', '-']symbol_priority[3] = ['*', '/']symbol_priority[4] = [')']def comparePriority(symbol, RPN_stack, symbol_stack):  '''Compare priority between two symbols'''  global symbol_priority  if len(symbol_stack) > 0:    symbol_pop = symbol_stack.pop()  else:    return  for list in symbol_priority.values():    if (symbol in list) and (symbol_pop in list):      '''same priority'''      symbol_stack.append(symbol_pop)      symbol_stack.append(symbol)      return    elif symbol in list:      '''symbol is smaller'''      RPN_stack.append(symbol_pop)      #recusion call      comparePriority(symbol, RPN_stack, symbol_stack)      return    elif symbol_pop in list:      '''symbol is bigger'''      symbol_stack.append(symbol_pop)      symbol_stack.append(symbol)      return    else:      continue    symbol_stack.append(symbol_pop)    returndef scanEveryone(input_string, RPN_stack, symbol_stack):  for ch in input_string:    if ch.isdigit():      RPN_stack.append(ch)    else:      if len(symbol_stack) > 0:        if ch == '(':          symbol_stack.append(ch)        elif ch == ')':          while True:            symbol_pop = symbol_stack.pop()            if symbol_pop == '(':              break            else:              RPN_stack.append(symbol_pop)        else:          comparePriority(ch, RPN_stack, symbol_stack)      else:        symbol_stack.append(ch)def scanInput(RPN_stack, symbol_stack):  input_string = raw_input()  input_string += '#'  scanEveryone(input_string, RPN_stack, symbol_stack)def calRPN(RPN_stack):  value_stack = []  RPN_stack.append('#')  for value in RPN_stack:    if value == '#':      return value_stack.pop()      break    if value.isdigit():      value_stack.append(value)    else:      right_value = value_stack.pop()      left_value = value_stack.pop()      cal_string = left_value + value + right_value      value_stack.append(str(eval(cal_string)))def main():  RPN_stack = []  symbol_stack = []  scanInput(RPN_stack, symbol_stack)  print calRPN(RPN_stack)if __name__ == '__main__':  main()

I hope this article will help you with Python programming.