Question

我有这个代码可以正常工作，但我无法弄清楚如何正确格式化。

from Stack import*

def main():

file=input("Enter the name of the file containing postfix expressions: ")
file=open(file, 'r')

stack=Stack()

operators=["/", "*", "-", "+"]

for line in file:

    try:

        print("Expression: " ,line)
        expression=line.split()
        for i in expression:
            if i not in operators:
                stack.push(i)

            if i == "/":
                x=int(stack.pop())
                y=int(stack.pop())
                stack.push(y/x)

            if i == "*":
                x=int(stack.pop())
                y=int(stack.pop())
                stack.push(x*y)

            if i == "+":
                x=int(stack.pop())
                y=int(stack.pop())
                stack.push(x+y)

            if i == "-":
                x=int(stack.pop())
                y=int(stack.pop())
                stack.push(y-x)

        if stack.size() > 1:
            print("Error: ",line,"is an invalid postfix expression")
        else:
            print("Answer: " ,stack.pop())


    except IndexError:
        print("Error: ",line,"is an invalid postfix expression.")
    except ValueError:
        print("Error: ",line,"is an invalid postfix expression.")
main()

但输出结果看起来像这样：我认为它看起来不错是非常重要的，但我希望它能够实现。

Enter the name of the file containing postfix expressions: expressions.txt
Expression:  5 4 3 + 2 * -

Answer:  -9
Expression:  8 5 *

Answer:  40
Expression:  20 5 /

Answer:  4.0
Expression:  3 8 6 + *

Answer:  42
Expression:  3 4 + 9 - 12 +

Answer:  10
Expression:  9 3 2 1 + + /

Answer:  1.5
Expression:  3 + 4

Error:  3 + 4
 is an invalid postfix expression.
Expression:  * 3 4 5 + *

Error:  * 3 4 5 + *
 is an invalid postfix expression.
Expression:  4 9 1 3 + -

Error:  4 9 1 3 + -
 is an invalid postfix expression
Expression:  h 3 +

Error:  h 3 +
 is an invalid postfix expression.

这里发生了什么？

Answer 1

在你的文件的字符串末尾可能会有一个\ n换行符。尝试使用python的str.strip（）函数剥离它。

Answer 2

这样的打印元素会为您提供听起来不需要的额外空间。

>>> print('a', 'b')
a b

所以，你想要改变

print("Error: ",line,"is an invalid postfix expression.")

到

print("Error:", line, "is an invalid postfix expression.")

同样，改变

print("Answer: " ,stack.pop())

到

print("Answer:", stack.pop())

注意：我已将逗号移到更标准的位置，但这种差异没有任何影响。

More information here, including how to use the end parameter.您可能也会受益于字符串格式化操作，有关可以找到的信息here。

有打印语句格式的问题

2 个答案: