Pythonで中置記法を逆ポーランド記法に変換して計算する

# 演算子のための定数
LEFT_ASSOC = 0
RIGHT_ASSOC = 1
 
# 対応する演算子
OPERATORS = {
    '+' : (0, LEFT_ASSOC),
    '-' : (0, LEFT_ASSOC),
    '*' : (5, LEFT_ASSOC),
    '/' : (5, LEFT_ASSOC),
    '%' : (5, LEFT_ASSOC),
    '^' : (10, RIGHT_ASSOC)
}
 
# 演算子かどうかの確認
def is_operator(token):
    return token in OPERATORS.keys()
 
# 結合性の確認
def is_associative(token, assoc):
    if not is_operator(token):
        raise ValueError('Invalid token: %s' % token)
    return OPERATORS[token][1] == assoc
 
# 二つの記号の優先順位を確認
def cmp_precedence(token1, token2):
    if not is_operator(token1) or not is_operator(token2):
        raise ValueError('Invalid tokens: %s %s' % (token1, token2))
    return OPERATORS[token1][0] - OPERATORS[token2][0]
 
# 中置記法を逆ポーランド記法に変換する
def infix_to_RPN(tokens):
    out = []
    stack = []
    for token in tokens:
        if is_operator(token):
            while len(stack) != 0 and is_operator(stack[-1]):
                if (is_associative(token, LEFT_ASSOC) and
                    cmp_precedence(token, stack[-1]) <= 0) or(
                    is_associative(token, RIGHT_ASSOC) and
                    cmp_precedence(token, stack[-1]) < 0):
                    out.append(stack.pop())
                    continue
                break
            stack.append(token)
        elif token == '(':
            stack.append(token)
        elif token == ')':
            while len(stack) != 0 and stack[-1] != '(':
                out.append(stack.pop())
            stack.pop()
        else:
            out.append(token)
    while len(stack) != 0:
        out.append(stack.pop())
    return out
 
# リストの要素をタブ区切りの文字列にする
def list_to_str_with_space(lst):
  str_w_space = '\t'.join([i for i in lst])
  return str_w_space

ops = {
  "+": (lambda a, b: a + b),
  "-": (lambda a, b: a - b),
  "*": (lambda a, b: a * b),
  "/": (lambda a, b: a / b),
  "^": (lambda a, b: a ** b)
}

# 逆ポーランド記法の数式を計算する
def calc_RPN(expression):
  tokens_RPN = expression.split()
  stack = []

  for token in tokens_RPN:
    if token in ops:
      arg2 = stack.pop()
      arg1 = stack.pop()
      result = ops[token](arg1, arg2)
      stack.append(result)
    else:
      stack.append(int(token))

  return stack.pop()

# 入力と出力のための関数
def in_and_out(input_equation):
    output = infix_to_RPN(input_equation.split(" "))
    stri = list_to_str_with_space(output)
    print(stri)
    result = calc_RPN(stri)
    print(result)

if __name__ == '__main__':
    in_and_out("( 1 + 2 ) * ( 3 / 4 ) ^ ( 5 + 6 )")
    in_and_out("( 2 + 3 ) * ( 4 / 5 ) ^ ( 6 + 7 )")
    in_and_out("( 7 + 6 ) * ( 5 / 4 ) ^ ( 3 + 2 )")

参考：
https://andreinc.net/2010/10/05/converting-infix-to-rpn-shunting-yard-algorithm/