问基本算术计算器

EN

import operator

priorizedOperators = operator.getPriorizedOperators()

def calculate(args):
    return _calculate(args,0)

def _calculate(equation, operatorArrayIndex):

    if len(priorizedOperators) == operatorArrayIndex:
        return equation;

    arithmeticOperator = priorizedOperators[operatorArrayIndex]
    copiedEquation = equation

    try:
        operatorLocation = copiedEquation.index(arithmeticOperator.getStringSign())

        while True:
            leftBound = _findLeftBound(equation,operatorLocation)
            rightBound = _findRightBound(equation,operatorLocation)

            leftValue = int(copiedEquation[leftBound:operatorLocation])
            rightValue = int(copiedEquation[operatorLocation+1:rightBound])

            temp = arithmeticOperator.operate(leftValue,rightValue)

            #Replaces the part of the equation we just computed by the result
            copiedEquation = copiedEquation[:leftBound] + str(temp) + copiedEquation[rightBound:]

            #This will throw an exception if index doesn't find the operator, which ends the while loop
            operatorLocation = copiedEquation.index(arithmeticOperator.getStringSign())
    finally:
        return _calculate(copiedEquation, operatorArrayIndex + 1)

def _findLeftBound(equation ,operatorIndex):
    for leftBoundSearchIndex in reversed(range(0,operatorIndex)):
        if not _isNumber(equation[leftBoundSearchIndex]):
            return leftBoundSearchIndex + 1

    return 0

def _findRightBound(equation, operatorIndex):
    for rightBoundSearchIndex in range(operatorIndex+1, len(equation)):
        if not _isNumber(equation[rightBoundSearchIndex]):
            return rightBoundSearchIndex

    return len(equation)

def _isNumber(char):
    return ord("0") <= ord(char) <= ord("9")

def main():
    equation = input("Enter equation : ")
    print(calculate(equation))

if __name__ == "__main__": main()

class PlusOperator():
    def getStringSign(self):
        return "+"

    def operate(self,left,right):
        return left + right

class MinusOperator():
    def getStringSign(self):
        return "-"

    def operate(self,left,right):
        return left - right

class MultiplyOperator():
    def getStringSign(self):
        return "*"

    def operate(self,left,right):
        return left * right

class DivideOperator():
    def getStringSign(self):
        return "/"

    def operate(self,left,right):
        return left // right

def getPriorizedOperators():
    return [MultiplyOperator(),DivideOperator(),PlusOperator(),MinusOperator()]