def solve_method(expression): st = [] res = [] flag = True i = len(expression) - 1 while i >= 0: if expression[i] == ")" or expression[i] == " " or expression[i] == "(": i -= 1 elif expression[i].isalpha(): op = expression[i - 2 : i + 1] st.append(op) i -= 3 else: space_index = expression.rfind(" ", 0, i) if space_index < 0 or ("a" <= expression[space_index + 1] <= "z"): space_index = expression.rfind("(", 0, i) num = expression[space_index + 1 : i + 1] st.append(num) i = space_index n = len(st) for j in range(n): s = st[j] if s == "add" or s == "sub" or s == "mul" or s == "div": if len(res) < 2: return num2 = res.pop() num1 = res.pop() result = 0 if s == "add": result = num1 + num2 elif s == "sub": result = num2 - num1 elif s == "mul": result = num1 * num2 elif s == "div": if num1 == 0: flag = False else: result = num2 // num1 res.append(result) else: res.append(int(s)) if not flag: print("error") else: print(res[-1]) expression = "(sub (mul 2 4) (div 9 3))" solve_method(expression) 加上注释
时间: 2024-02-14 12:29:43 浏览: 26
下面是添加了注释的修改后的代码:
```python
def solve_method(expression):
st = [] # 存储操作符和操作数
res = [] # 存储计算结果
flag = True # 标志变量,用于判断是否发生错误
i = len(expression) - 1
while i >= 0:
if expression[i] == ")" or expression[i] == " " or expression[i] == "(":
i -= 1
elif expression[i].isalpha(): # 如果是字母,则说明是操作符
op = expression[i - 2: i + 1] # 获取操作符
st.append(op) # 将操作符存入栈中
i -= 3
else: # 如果是数字
space_index = expression.rfind(" ", 0, i)
if space_index < 0 or ("a" <= expression[space_index + 1] <= "z"):
space_index = expression.rfind("(", 0, i)
num = expression[space_index + 1: i + 1] # 获取数字
st.append(num) # 将数字存入栈中
i = space_index
n = len(st)
for j in range(n):
s = st[j]
if s == "add" or s == "sub" or s == "mul" or s == "div":
if len(res) < 2: # 如果栈中元素少于2个,说明表达式有误
return
num2 = res.pop() # 弹出栈顶的操作数2
num1 = res.pop() # 弹出栈顶的操作数1
result = 0
if s == "add":
result = num1 + num2
elif s == "sub":
result = num2 - num1
elif s == "mul":
result = num1 * num2
elif s == "div":
if num1 == 0:
flag = False
else:
result = num2 // num1
res.append(result) # 将计算结果存入栈中
else:
res.append(int(s)) # 如果是数字,将其转换为整数并存入栈中
if not flag:
print("error")
else:
print(res[-1]) # 输出最终计算结果
expression = "(sub (mul 2 4) (div 9 3))"
solve_method(expression)
```
这段代码可以正确地计算给定的表达式 `(sub (mul 2 4) (div 9 3))` 并输出结果。如果表达式有误或发生除零错误,将打印出相应的错误信息。
希望这次的修改能够满足你的需求!如果还有其他问题,请随时提问。