Python：想捕捉异常，但不知道它来自哪里？ [英] Python: want to catch exception, but don't know where it comes from?

问题描述

我正在使用Django教程学习Python，我有这个代码

I'm learning Python using the Django tutorial, and I have this code

poll = Poll.objects.get(pk = poll_id)

当poll_id不在数据库中时，我得到一个DoesNotExist异常，这很好，因为该教程告诉我要执行以下操作：

When poll_id is not in the database I get a DoesNotExist exception, which is fine because the tutorial tells me to do the following:

try:
    poll = Poll.objects.get(pk = poll_id)
except Poll.DoesNotExist:
    raise Http404

我的问题是：if我没有帮助我的教程，下面的堆栈跟踪怎么知道DoesNotExist异常是Poll的一部分？

My question is: if I didn't have the tutorial to help me, how would I, given the stack trace below, have known that the DoesNotExist exception is part of Poll?

（即我的猜测是将'DoesNotExist：除外）告诉我：全局名称'DoesNotExist'未定义）

(i.e. my guess would have been to put 'except DoesNotExist:' and this would have told me: "global name 'DoesNotExist' is not defined")

Request Method: GET
Request URL: http://127.0.0.1:8000/polls/3/

Django Version: 1.6.2
Python Version: 2.7.2
Installed Applications:
('django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'polls')
Installed Middleware:
('django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware')


Traceback:
File "/Library/Python/2.7/site-packages/django/core/handlers/base.py" in get_response
  114.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/tom/Documents/dev/django-test/mysite/polls/views.py" in detail
  26.   poll = Poll.objects.get(pk = poll_id)
File "/Library/Python/2.7/site-packages/django/db/models/manager.py" in get
  151.         return self.get_queryset().get(*args, **kwargs)
File "/Library/Python/2.7/site-packages/django/db/models/query.py" in get
  307.                 self.model._meta.object_name)

Exception Type: DoesNotExist at /polls/3/
Exception Value: Poll matching query does not exist.

全新的python。我明显地缺少一些明显的东西。

Totally new to python. I'm obviously missing something obvious.

推荐答案

你不会知道;您必须查看项目文档或抛出异常的代码

You wouldn't have known; you'd have to look at the project documentation or the code throwing the exception.

请注意， Model.DoesNotExist 引用是一个方便，因此您不必导入异常。你不会从抛出异常的代码中推断出这一点。这个特殊的Django异常对象是 django.core.exceptions.ObjectDoesNotExist 根据模型自定义。

Note that the Model.DoesNotExist reference is a convenience so you don't have to import the exception either. You wouldn't deduce this from the code throwing the exception. This special Django exception object is a subclass of django.core.exceptions.ObjectDoesNotExist customized per model.

一般来说，您可以捕获异常并查看异常捕获的模块：

In general, you could catch Exception and look at the module of the exception caught:

except Exception as e:
    print type(e), type(e).__module__

这将告诉你什么模块定义了例外情况，您可以选择将来从中导入。

This would tell you what module the exception is defined in, giving you the option to import it from there in future.

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