你如何静态输入一个变量，所以它只需要一个大于 0 的整数

Question

我想要做的是创建一个名为Pizza的类，它接受 2 个输入： self和radius如果您创建Pizza的实例，您在其中输入任何radius而不是大于 0 的整数，它将打印一条语句: 'Sorry, but that is an invalid input. A valid input is any integer greater than 0.' 'Sorry, but that is an invalid input. A valid input is any integer greater than 0.'

到目前为止，这是我的Pizza课程，但我想进行更改，以便上述内容正确：

class Pizza:
    def __init__(self, radius):
        self.radius = radius

Answer 1

利用Python 的错误和异常处理可能是一种更灵活的方法。

不是在类定义中硬编码错误响应（即打印出错误字符串），而是通知调用者发生了错误条件，然后可以对该上下文进行适当的操作（即在控制台，生成图形错误提示，忽略错误，尝试不同的输入等）。

class Pizza:
    def __init__(self, radius):
        if not isinstance(radius, int):
            raise ValueError('radius must be an integer')
        if not radius > 0:
            raise ValueError('radius must be greater than 0')
        self.radius = radius

inputs = [8, -8, 8.8, '8', 'foo']

print('\nTesting inputs and outputting error messages:')
for r in inputs:
    print('r: {} ({})'.format(r, type(r)))
    try:
        p = Pizza(r)
    except ValueError as e:
        print('Unable to create Pizza: {}'.format(e))
        continue
    print('p.radius: {}'.format(p.radius))

print('\nTesting inputs and silently discarding errors:')
for r in inputs:
    print('r: {} ({})'.format(r, type(r)))
    try:
        p = Pizza(r)
    except ValueError as e:
        continue
    print('p.radius: {}'.format(p.radius))

输出

$ python3 pizza.py

Testing inputs and outputting error messages:
r: 8 (<class 'int'>)
p.radius: 8
r: -8 (<class 'int'>)
Unable to create Pizza: radius must be greater than 0
r: 8.8 (<class 'float'>)
Unable to create Pizza: radius must be an integer
r: 8 (<class 'str'>)
Unable to create Pizza: radius must be an integer
r: foo (<class 'str'>)
Unable to create Pizza: radius must be an integer

Testing inputs and silently discarding errors:
r: 8 (<class 'int'>)
p.radius: 8
r: -8 (<class 'int'>)
r: 8.8 (<class 'float'>)
r: 8 (<class 'str'>)
r: foo (<class 'str'>)

Answer 2

这可以通过

class Pizza:
     def __init__(self, radius):
            if isinstance(radius, int) and radius > 0 :
                self.radius = radius
            else:
                print('Sorry,  but that is an invalid input. A valid input is any integer greater than 0.')