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.
这篇关于Python：想捕捉异常，但不知道它来自哪里？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！