如何使用整数验证计算器程序的运算符？

Question

我正在尝试创建一个程序，允许用户输入 4 个运算符（加、减、乘或除）之一，然后输入两个数字。然后程序计算操作。不过，我似乎无法验证输出的运算符。我现在正在尝试使用if...else声明，但没有运气。这里有什么指点吗？operator = ""numbers = []inputNumbers = ["first number", "second number"]def userInput():    try:        operator = input("Please choose a valid operation (+, -, *, /): ")    except:        print("Please enter a valid operator.")    for inputNumber in inputNumbers:        user_num_input = -1        while user_num_input < 0:            try:                user_num_input = int(input("Type in {}: ".format(inputNumber)))            except:                user_num_input = -1                print("Please enter a whole number.")            if user_num_input > -1:                numbers.append(user_num_input)userInput()def addNumbers():    add = numbers[0] + numbers[1]    return add(numbers)def subNumbers():    sub = numbers[0] - numbers[1]    return sub(numbers)def mulNumbers():    mul = numbers[0] * numbers[1]    return mul(numbers)def divNumbers():    div = numbers[0] / numbers[1]    return div(numbers)def userOutput():    if operator == "+":        print(numbers[0], "+", numbers[1], "=", addNumbers())    elif operator == "-":        print(numbers[0], "-", numbers[1], "=", subNumbers())    elif operator == "*":        print(numbers[0], "*", numbers[1], "=", mulNumbers())    elif operator == "/":        print(numbers[0], "/", numbers[1], "=", divNumbers())userOutput()

Answer 1

您应该检查用户是否输入了有效的操作，try except因为input()不会抛出任何错误，所以在这里不起作用。还有更优雅的方法可以从用户那里获取 2 个有效整数，并计算最终方程（使用eval()）

inputNumbers = ["first number", "second number"]

operations = ['+', '-', '*', '/']

numbers = []

operator = ''

while not operator:

    operator = input('Please choose a valid operation (+, -, *, /): ')

    if operator not in operations:

        print("Please enter a valid operator.")

while len(numbers) < len(inputNumbers):

    try:

        numbers.append(int(input("Type in {}: ".format(inputNumbers[len(numbers)]))))

    except:

        print("Please enter a whole number.")

result = eval(operator.join(map(str, numbers)))

print('{} {} {} = {}'.format(numbers[0], operator, numbers[1], result))

输出：

Please choose a valid operation (+, -, *, /): addition

Please enter a valid operator.

Please choose a valid operation (+, -, *, /): /

Type in first number: 123.321

Please enter a whole number.

Type in first number: 10 

Type in second number: hundred

Please enter a whole number.

Type in second number: 100

10 / 100 = 0.1

Answer 2

您应该使用python的内置operator 模块。然后你可以使用这样的字典：

import operator

operator_dict = {"+": operator.add, 

                 "-": operator.sub, 

                 "*": operator.mul,

                 "/": operator.truediv}

user_input = input("Please choose a valid operation (+, -, *, /): ")

operator_func = operator_dict.get(user_input, None)

# if operator_func is not None then the input was correct!

if operator_func is not None:

    ... get the numbers ...

    print("{}{}{}={}".format(num1, user_input, num2, operator_func(num1, num2))

这样您就不需要自己实现简单的运算符功能。

Answer 3

最简单和最干净的方法是使用operatorPython 中的模块，因此您的userOutput方法将如下所示。但是，您应该对代码进行一些更改，将小时operator变量重命名为op，因为它会与 python 模块名称冲突，并将 更新operator为从 的返回userInput()：

import operator

op = ""

numbers = []

inputNumbers = ["first number", "second number"]

operators = {

        '+' : operator.add,

        '-' : operator.sub,

        '*' : operator.mul,

        '/' : operator.truediv,

        '%' : operator.mod,

        '^' : operator.xor,

}

def userInput(op):

    while not op:

        op = input("Please choose a valid operation (+, -, *, /): ")

        if op not in operators:

            print("Please enter a valid operator.")

            op = ""

    for inputNumber in inputNumbers:

        user_num_input = -1

        while user_num_input < 0:

            try:

                user_num_input = int(input("Type in {}: ".format(inputNumber)))

            except:

                user_num_input = -1

                print("Please enter a whole number.")

            if user_num_input > -1:

                numbers.append(user_num_input)

    return op

def userOutput(op, operators):

    result = operators[op](numbers[0], numbers[1])

    print("{} {} {} = {}". format(numbers[0], op, numbers[1], result))

op = userInput(op)

userOutput(op, operators)