我正在编写程序,正在将函数转换为前缀并进行计算。
from pythonds.basic import Stack
def doMath(op, op1, op2):
if op == "*":
return int(op1) * int(op2)
elif op == "/":
return int(op1) / int(op2)
elif op == "+":
return int(op1) + int(op2)
elif op == "-":
return int(op1) + int(op2)
def postfixEval(postfixExpr):
operandStack = Stack()
tokenList = postfixExpr.split()
for token in tokenList:
print(tokenList)
print("this is token: ", token)
if token in "0123456789":
operandStack.push(token)
print("pop: ",operandStack.peek())
elif not operandStack.isEmpty():
operand2 = operandStack.pop()
operand1 = operandStack.pop()
result = doMath(token, operand1, operand2)
print (result)
operandStack.push(result)
return operandStack.pop()
print(postfixEval('7 8 + 3 2 + /'))
print(postfixEval("17 10 + 3 * 9 /"))
所以当我运行第一个postfixEval时,它返回3.0,但在第二次打印时返回IndexError: pop from empty list
显然是2位数的BC,我该如何解决?
谢谢
用if token in "0123456789"
替换if token.isdigit():
。