How to do math operations with string?

Question

If a have the string calculation = '1+1x8'. How can I convert this into calculation = 1+1*8? I tried doing something like

for char in calculation:
    if char == 'x':
        calculation = calculation.replace('x', *)

    # and

    if char == '1':
        calculation = calculation.replace('1', 1)

This clearly doesn't work, since you can't replace just one character with an integer. The entire string needs to be an integer, and if I do that it doesn't work either since I can't convert 'x' and '+' to integers

Answer 1

让我们用更复杂的字符串作为一个例子：1+12x8。接下来是一个粗略的概述；您需要为每个步骤提供实施。

首先，将其标记化，1+12x8变成['1', '+', '12', 'x', '8']。对于这一步，您需要编写一个标记器或一个词法分析器。这是定义运算符和文字的步骤。

接下来，将令牌流转换为解析树。也许您将树表示为S表达式 ['+', '1', ['x', '12', '8']]或[operator.add, 1, [operator.mul, 12, 8]]。此步骤需要编写一个解析器，该解析器需要定义诸如运算符优先级之类的东西。

最后，您编写了一个评估程序，可以将您的解析树减少为单个值。分两步执行可能会产生

1. [operator.add, 1, [operator.mul, 12, 8]] 至 [operator.add, 1, 96]
2. [operator.add, 1, 96] 至 97