python - 使用基本的 python 计算器，但无法让我的菜单正确循环

Question

多亏了这个网站，作为一个Python新手，我才能够走到这一步，但是我有点卡住了。我正在尝试循环“选择”，因此在用户进行一些数学运算后，而不是仅仅结束它，他们可以选择执行其他操作，直到他们选择 0 退出。我尝试了很多其他尝试和条件语句，但最终只得到答案并陷入无限循环。

另外，我在这里很漂亮，但感谢任何帮助，而且我也是一个 python nub。我正在用 python 2.7 写这篇文章，如果这很重要的话。

def sum ( arg1, arg2):
 total = a + b
 return total;

def subtract ( arg1 , arg2):
     total = a - b
     return total;

def mult ( arg1, arg2):
     total = a * b
     return total;

def division ( arg1, arg2):
     total = (a / b) 
     return total;



options = ["1", "2", "3", "4", "5", "0"]

print ("Please choose an option for mathing")
print ("1 for addition")
print ("2 for division")
print ("3 for subtraction")
print ("4 for multiplication")
print ("5 ")
print ("0 to exit")


#this will keep prompting the user to provide an input that is listed in 'options'
while True:
    selection = input("Please select choose an option to continue")
    if selection in options:
        break

    else:
        print("Please choose a valid option")

#user input for mathing
#input will be validated as follows
a = None
while a is None:
  try:
     a = int(input("please provide a number for A"))
  except ValueError:
     print "please use a valid integer"
     pass

b = None
while b is None:
  try:
     b = int(input("please provide a number for B"))
  except ValueError:
    print "please use a valid integer"
    pass


#performing the operations

if selection == '1':
    print "The sum is", str(sum(a, b))

elif selection == '2':
    print "The quotient is", str(division(a, b))

elif selection == '3':
    print "The difference is", str(subtract(a, b))

elif selection == '4':
    print "The product is", str(mult(a, b))

elif selection == '0':
    exit()

Answer 1

为了提高效率，我会做一些事情..

options 应该是一本字典...你的 in 在字典上比在列表上更有效。这样做的好处是每个键的值都可以是函数方法。

例如。 options = {1: '求和', 2: '减去' ..... }

然后创建一个包含数学运算的类

class Calculator(object):

    def sum(self, x, y):
        return x + y
    def subtract(self, x, y):
        return x - y

    #add more operations here

    @staticmethod
    def start():
        while True:
            #prompt for input and the operator

这样做的好处是，在检查选择时，您可以动态调用类方法来清理大量代码

if selection in options:
    getattr(options[selection], Calculator)(a, b)

如果你想让我解释更多，我可以完成这个例子。

对于循环，您可以添加一个方法来启动操作并继续循环并每次执行更多操作

这是一个基本类，您可以使用我描述的那些方法来使用

class Calculator(object):
    loop = None
    calculations = 1
    current_value = 0
    selection = 0
    options = {1: 'add', 2: 'subtract', 3: 'multiply', 4: 'divide'}

    def __init__(self, loop=True):
        self.loop = loop
        print 'Welcome to my basic calculator!'
        if not self.loop: # dont loop just execute once
            self.run()
        else:
            while True:
                self.run()

    @staticmethod
    def add(x, y):
        return x + y

    @staticmethod
    def subtract(x, y):
        return x - y

    @staticmethod
    def multiply(x, y):
        return x * y

    @staticmethod
    def divide(x, y):
        if y != 0: #cant divide by 0
            return x / y 

    @staticmethod
    def quit():
        exit(0)

    def run(self):
        if self.calculations == 1:
            self.current_value = self.prompt_user_input('please provide a number: ')

        self.prompt_operator('Please choose an operator to continue\n1 for addition\n2 for subtraction\n3 for multiplication \n4 for division\n0 to quit\n')
        y = self.prompt_user_input('please provide a number: ')
        self.current_value = getattr(Calculator, self.options[self.selection])(self.current_value,y)
        self.calculations += 1

        print 'New value is: ' + str(self.current_value)

    def prompt_operator(self, prompt_message):
        while True:
            self.selection = input(prompt_message)
            if self.selection in self.options:
                break
            elif self.selection == 0:
                self.quit()
            else:
                print("Please choose a valid option")

    def prompt_user_input(self, prompt_message):
        val = None
        while val is None:
            try:
                val = int(input(prompt_message))
            except ValueError:
                print "please use a valid integer"
                pass
        return val

最后，要启动计算器，您只需调用它并传递 true 继续循环或传递 false 只进行一次计算

Calculator(loop=True)