OOP / try except init of class 中的语句

Question

我想控制classWebpage的输入。意思是，我想确保适当地提供了网页的 link，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)

然而，当我尝试代码时：

test_link = Webpage('example.com')

我没有得到 ValueError，正如我所期望的。方法调用：

test_link.get_link()
print(test_lint)

结果

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

这表示 try/except 部分工作 - try 没有执行 self.link = link，但是 except 语句没有执行。

一个例子：

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

与 class 的 get_link() 和 print 方法配合使用效果很好。

感谢任何提示。

Answer 1

在 try 块中提出 ValueError 的期望值，并在 except 块中处理期望值

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

希望对您有所帮助

Answer 2

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

如果您传递 link example.com，if 语句失败，因为它不包含任何前面提到的前缀。由于它在逻辑上是正确的，它永远不会下降到 except 块。您可能想检查 self.link 是否存在于 get_link 函数

中

Answer 3

试试这个更新后的代码

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)

Answer 4

您可以使用 str.startswith 和 str.endswith 并在 else 中创建 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())

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