Question

我想控制类Webpage的输入。意思是，我想确保网页的链接是正确提供的，例如'http://example.com'。

class Webpage(object):
    def __init__(self, link):
        prefix = ['http', 'https']
        suffix = ['com', 'net']
        try:
            if link.split(':')[0] in prefix and link.split('.')[-1] in suffix:
                self.link = link
        except:
            raise ValueError('Invalid link') 


   def get_link(self):
        '''
        Used to safely access self.link outside of the class

        Returns: self.link
        '''
        return self.link

   def __str__(self):
        return str(self.link)

但是，当我尝试代码时：

test_link = Webpage('example.com')

我没有得到ValueError的期望。方法调用：

test_link.get_link()
print(test_lint)

导致

AttributeError: 'Webpage' object has no attribute 'link'

表示try / except部分起作用-try未执行self.link = link，但是未执行except语句。

一个例子：

test_link = Webpage('http://example.com')

可以与该类的get_link()和print方法一起正常工作。

将不胜感激。

Answer 1

您可以使用str.startswith和str.endswith并在其他地方创建raise。

演示：

class Webpage(object):
    def __init__(self, link):
        prefix = ('http', 'https')
        suffix = ('com', 'net')
        if (link.startswith(prefix)) and (link.endswith(suffix)):
            self.link = link
        else:
            raise ValueError('Invalid link') 

    def get_link(self):
        '''
        Used to safely access self.link outside of the class

        Returns: self.link
        '''
        return self.link

    def __str__(self):
        return str(self.link)  

test_link = Webpage( 'example.com')
print(test_link.get_link())

Answer 2

在您的情况下提高期望值，在try块中完成ValueError，而在except块中完成期望的处理

有关更多信息，请访问Raising Expections in python

class Webpage(object):
    def __init__(self, link):
        prefix = ['http', 'https']
        suffix = ['com', 'net']
        try:
            if link.split(':')[0] in prefix and link.split('.')[-1] in suffix:

                self.link = link
            else:
                raise ValueError('Invalid link')
        except ValueError as exp:
            print("the value error is {}\nthe link specified is {} ".format(exp,link))



    def get_link(self):
        '''
        Used to safely access self.link outside of the class

        Returns: self.link
        '''
        return self.link

    def __str__(self):
        return str(self.link) 

test_link = Webpage('example.com')

输出

the value error is Invalid link
the link specified is example.com

希望这会有所帮助

Answer 3

 try:
            if link.split(':')[0] in prefix and link.split('.')[-1] in suffix:
                self.link = link
        except:
            raise ValueError('Invalid link')

如果传递链接example.com，则if语句失败，因为它不包含任何前面提到的前缀。由于其逻辑上正确，因此它将永远不会下降到except块。您可能需要检查self.link函数中是否存在get_link

Answer 4

尝试此更新的代码

class Webpage(object):
    def __init__(self, link):
        prefix = ['http', 'https']
        suffix = ['com', 'net']
        if link.split(':')[0] in prefix and link.split('.')[-1] in suffix:
            self.link = link
        else:
            self.link = 'Invalid link'


    def get_link(self):
        '''
        Used to safely access self.link outside of the class

        Returns: self.link
        '''
        return self.link

    def __str__(self):
        return str(self.link)

test_link = Webpage('example.com')
test_link.get_link()
print(test_link)

OOP /尝试使用类

4 个答案: