一个例外只是一个加注有什么用吗？ [英] Does a exception with just a raise have any use?

问题描述

例如，这里是django.templates.loader.app_directories.py的一些代码。[1]

For example, here is some code from django.templates.loader.app_directories.py.[1]

try:
    yield safe_join(template_dir, template_name)
except UnicodeDecodeError:
    # The template dir name was a bytestring that wasn't valid UTF-8.
    raise

如果你捕获一个异常，只是为了提高它，它的目的是什么？

If you catch an exception just to re raise it, what purpose does it serve?

[1] http://code.djangoproject.com/browser/django/trunk/django/template/loaders/app_directories.py

推荐答案

在您链接的代码中，另外还有一个异常处理程序：

In the code you linked to is another additional exception handler:

try:
    yield safe_join(template_dir, template_name)
except UnicodeDecodeError:
    # The template dir name was a bytestring that wasn't valid UTF-8.
    raise
except ValueError:
    # The joined path was located outside of template_dir.
    pass

由于 UnicodeDecodeError 是 ValueError的子类，第二个异常处理程序将导致任何 UnicodeDecodeError 被忽略。看起来这不是预期的效果，并且避免它由第一个处理程序显式处理的 UnicodeDecodeError 。因此，两个处理程序一起，$ code> ValueError 仅在不是 UnicodeDecodeError 时被忽略。

Since UnicodeDecodeError is a subclass of ValueError, the second exception handler would cause any UnicodeDecodeError to be ignored. It looks like this would not be the intended effect and to avoid it the UnicodeDecodeError is processed explicitly by the first handler. So with both handlers together a ValueError is only ignored if it's not a UnicodeDecodeError.

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