Python：另一个“NoneType”对象没有属性错误 [英] Python : Another 'NoneType' object has no attribute error

问题描述

对于新手练习，我试图在html文件中找到元标记，并提取生成器，以便我这样做：

For a newbie exercise , I am trying to find the meta tag in a html file and extract the generator so I did like this :

Version = soup.find("meta", {"name":"generator"})['content']

，因为我有这个错误：

TypeError: 'NoneType' object has no attribute '__getitem__'

我以为使用异常会纠正它，所以我写道：

I was thinking that working with exception would correct it, so I wrote :

try: Version = soup.find("meta", {"name":"generator"})['content']

except NameError,TypeError:

     print "Not found"

我所得到的是同样的错误。

and what I got is the same error.

那么该怎么办？

推荐答案

soup.find（）方法没有找到匹配标签，并返回无。

The soup.find() method did not find a matching tag, and returned None.

[...] 项目访问语法查找 __ getitem __ 方法，这是 AttributeError 的源代码：

The [...] item access syntax looks for a __getitem__ method, which is the source of the AttributeError here:

>>> None[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object has no attribute '__getitem__'

测试无显式：

Version = soup.find("meta", {"name":"generator"})
if Version is not None:
    Version = Version['content']
else:
    print "Not found"

如果您使用括号对异常进行分组，则您的异常处理也可以正常工作：

Your exception handling would work too, provided you use parenthesis to group the exceptions:

try:
    Version = soup.find("meta", {"name":"generator"})['content']
except (NameError, TypeError):
    print "Not found"

没有括号，你告诉Python catch NameError 异常，并将生成的异常对象分配给本地名称 TypeError 。这个除了异常，名称：语法已经被弃用，因为它可以导致你的情况，你认为你抓住了两个例外。

Without parenthesis you are telling Python to catch NameError exceptions and assign the resulting exception object to the local name TypeError. This except Exception, name: syntax has been deprecated because it can lead to exactly your situation, where you think you are catching two exceptions.

但是，这里的代码不应该抛出一个 NameError exception;这将是一个单独的问题，更好地通过实例化你的变量来解决;以下内容也同样适用：

However, your code here should not throw a NameError exception; that'd be a separate problem better solved by instantiating your variables properly; the following would work just as well here:

try:
    Version = soup.find("meta", {"name":"generator"})['content']
except TypeError:
    # No such meta tag found.
    print "Not found"

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