逆ポーランド記法の構文解析やってみた

reverse_polish_notation.py

in_txt = '13 5 4 + 3 / 4 * -'.split(' ')
symbols = ('+', '-', '*', '/')
stack = []
print("input::", ' '.join(in_txt))

for i,_ in enumerate(in_txt):
    # FOUND NUM
    if in_txt[i] not in symbols:
        stack.append(int(in_txt[i]))
        continue

    # FOUND SYMBOL
    cur = in_txt[i]
    num1 = stack.pop()
    num2 = stack.pop()
    tmp = eval(f'{num2} {cur} {num1}')
    stack.append(tmp)

    print(f'{num2} {cur} {num1}')
    print("stack::", stack)

print("answer::", stack[-1])

実行結果：

$ python3 reverse_polish_notation.py
input:: 13 5 4 + 3 / 4 * -
5 + 4
stack:: [13, 9]
9 / 3
stack:: [13, 3.0]
3.0 * 4
stack:: [13, 12.0]
13 - 12.0
stack:: [1.0]
answer:: 1.0