当使用堆栈评估infix表达时，算术上的评估和键盘错误;

Question

我的程序应该评估给定的infix表达式并评估它们。假定只有代码底部的方法调用中的操作员才能用于该程序运行的任何给定的infix表达式。

from pythonds.basic.stack import Stack
import operator
def infixToValue(expr):
    prec = {}
    prec["*"] = 3
    prec["/"] = 3
    prec["+"] = 2
    prec["-"] = 2
    prec["≤"] = 1
    prec["$"] = 0
    opStack = Stack()
    valStack = Stack()
    ops = {"+": operator.add, "-": operator.sub, "*": operator.mul, "/": operator.truediv, "≤": operator.le}
    opList = ["+", "-", "*", "/", "≤"]
    tokens = expr.split()
    def doOp():
        x = int(valStack.pop())
        y = int(valStack.pop())
        op = ops[opStack.pop()]
        valStack.push(op(x, y))
    def repeatOps(refOp):
        while valStack.size() > 1 and opStack.size() > 0 and prec[refOp] <= prec[opStack.peek()]:
            doOp()
    for token in tokens:
        if token.isdigit():
            valStack.push(token)
        else:
            repeatOps(token)
            opStack.push(token)
    repeatOps("$")
    return valStack.pop()

print(infixToValue('14 - 3 * 2 + 7'))
print(infixToValue('14  ≤  4  -  3  *  2  +  7'))
print(infixToValue('15 + 16 – 2 + 7 * 3 * 2 – 14'))

当前输出如下：

C:UsersskarlAppDataLocalProgramsPythonPython37python.exe C:/Users/skarl/PycharmProjects/Project02/Root.py
Traceback (most recent call last):
  File "C:/Users/skarl/PycharmProjects/Project02/Root.py", line 40, in <module>
-1
    print(infixToValue('15 + 16 – 2 + 7 * 3 * 2 – 14'))
True
  File "C:/Users/skarl/PycharmProjects/Project02/Root.py", line 32, in infixToValue
    repeatOps(token)
  File "C:/Users/skarl/PycharmProjects/Project02/Root.py", line 25, in repeatOps
    while valStack.size() > 1 and opStack.size() > 0 and prec[refOp] <= prec[opStack.peek()]:
KeyError: '–'
Process finished with exit code 1

-1似乎是第一个infix表达式的结果，算术上是不正确的，也是我的" - "的键盘，这是在第一个infix表达式中引用的第二个表达式。哪些缺陷使我的代码工作不正确？

Answer 1

您的第三个呼叫中的–字符：

print(infixToValue('15 + 16 – 2 + 7 * 3 * 2 – 14'))

实际上是Unicode U 2013字符（en Dash）。

如果您用ASCII -符号替换两个EN DASH字符，则您的代码可以正常工作：

print(infixToValue('15 + 16 - 2 + 7 * 3 * 2 - 14'))