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This patch does not remove all occurrences of the words in question. Rather, I went through all of the occurrences of the words listed below, and judged if they a) suggested the reader had some kind of knowledge/experience, and b) if they added anything of value (including tone of voice, etc). I left most of the words alone. I looked at the following words: - simply/simple - easy/easier/easiest - obvious - just - merely - straightforward - ridiculous Thanks to Carlton Gibson for guidance on how to approach this issue, and to Tim Bell for providing the idea. But the enormous lion's share of thanks go to Adam Johnson for his patient and helpful review.
205 lines
7.3 KiB
Plaintext
205 lines
7.3 KiB
Plaintext
=============
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Writing views
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=============
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A view function, or *view* for short, is a Python function that takes a
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Web request and returns a Web response. This response can be the HTML contents
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of a Web page, or a redirect, or a 404 error, or an XML document, or an image .
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. . or anything, really. The view itself contains whatever arbitrary logic is
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necessary to return that response. This code can live anywhere you want, as long
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as it's on your Python path. There's no other requirement--no "magic," so to
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speak. For the sake of putting the code *somewhere*, the convention is to
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put views in a file called ``views.py``, placed in your project or
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application directory.
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A simple view
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=============
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Here's a view that returns the current date and time, as an HTML document::
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from django.http import HttpResponse
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import datetime
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def current_datetime(request):
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now = datetime.datetime.now()
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html = "<html><body>It is now %s.</body></html>" % now
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return HttpResponse(html)
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Let's step through this code one line at a time:
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* First, we import the class :class:`~django.http.HttpResponse` from the
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:mod:`django.http` module, along with Python's ``datetime`` library.
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* Next, we define a function called ``current_datetime``. This is the view
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function. Each view function takes an :class:`~django.http.HttpRequest`
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object as its first parameter, which is typically named ``request``.
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Note that the name of the view function doesn't matter; it doesn't have to
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be named in a certain way in order for Django to recognize it. We're
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calling it ``current_datetime`` here, because that name clearly indicates
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what it does.
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* The view returns an :class:`~django.http.HttpResponse` object that
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contains the generated response. Each view function is responsible for
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returning an :class:`~django.http.HttpResponse` object. (There are
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exceptions, but we'll get to those later.)
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.. admonition:: Django's Time Zone
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Django includes a :setting:`TIME_ZONE` setting that defaults to
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``America/Chicago``. This probably isn't where you live, so you might want
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to change it in your settings file.
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Mapping URLs to views
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=====================
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So, to recap, this view function returns an HTML page that includes the current
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date and time. To display this view at a particular URL, you'll need to create a
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*URLconf*; see :doc:`/topics/http/urls` for instructions.
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Returning errors
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================
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Django provides help for returning HTTP error codes. There are subclasses of
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:class:`~django.http.HttpResponse` for a number of common HTTP status codes
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other than 200 (which means *"OK"*). You can find the full list of available
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subclasses in the :ref:`request/response <ref-httpresponse-subclasses>`
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documentation. Return an instance of one of those subclasses instead of a
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normal :class:`~django.http.HttpResponse` in order to signify an error. For
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example::
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from django.http import HttpResponse, HttpResponseNotFound
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def my_view(request):
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# ...
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if foo:
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return HttpResponseNotFound('<h1>Page not found</h1>')
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else:
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return HttpResponse('<h1>Page was found</h1>')
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There isn't a specialized subclass for every possible HTTP response code,
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since many of them aren't going to be that common. However, as documented in
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the :class:`~django.http.HttpResponse` documentation, you can also pass the
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HTTP status code into the constructor for :class:`~django.http.HttpResponse`
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to create a return class for any status code you like. For example::
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from django.http import HttpResponse
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def my_view(request):
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# ...
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# Return a "created" (201) response code.
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return HttpResponse(status=201)
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Because 404 errors are by far the most common HTTP error, there's an easier way
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to handle those errors.
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The ``Http404`` exception
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-------------------------
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.. class:: django.http.Http404()
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When you return an error such as :class:`~django.http.HttpResponseNotFound`,
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you're responsible for defining the HTML of the resulting error page::
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return HttpResponseNotFound('<h1>Page not found</h1>')
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For convenience, and because it's a good idea to have a consistent 404 error page
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across your site, Django provides an ``Http404`` exception. If you raise
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``Http404`` at any point in a view function, Django will catch it and return the
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standard error page for your application, along with an HTTP error code 404.
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Example usage::
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from django.http import Http404
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from django.shortcuts import render
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from polls.models import Poll
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def detail(request, poll_id):
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try:
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p = Poll.objects.get(pk=poll_id)
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except Poll.DoesNotExist:
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raise Http404("Poll does not exist")
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return render(request, 'polls/detail.html', {'poll': p})
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In order to show customized HTML when Django returns a 404, you can create an
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HTML template named ``404.html`` and place it in the top level of your
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template tree. This template will then be served when :setting:`DEBUG` is set
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to ``False``.
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When :setting:`DEBUG` is ``True``, you can provide a message to ``Http404`` and
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it will appear in the standard 404 debug template. Use these messages for
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debugging purposes; they generally aren't suitable for use in a production 404
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template.
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.. _customizing-error-views:
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Customizing error views
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=======================
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The default error views in Django should suffice for most Web applications,
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but can easily be overridden if you need any custom behavior. Specify the
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handlers as seen below in your URLconf (setting them anywhere else will have no
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effect).
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The :func:`~django.views.defaults.page_not_found` view is overridden by
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:data:`~django.conf.urls.handler404`::
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handler404 = 'mysite.views.my_custom_page_not_found_view'
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The :func:`~django.views.defaults.server_error` view is overridden by
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:data:`~django.conf.urls.handler500`::
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handler500 = 'mysite.views.my_custom_error_view'
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The :func:`~django.views.defaults.permission_denied` view is overridden by
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:data:`~django.conf.urls.handler403`::
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handler403 = 'mysite.views.my_custom_permission_denied_view'
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The :func:`~django.views.defaults.bad_request` view is overridden by
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:data:`~django.conf.urls.handler400`::
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handler400 = 'mysite.views.my_custom_bad_request_view'
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.. seealso::
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Use the :setting:`CSRF_FAILURE_VIEW` setting to override the CSRF error
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view.
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Testing custom error views
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--------------------------
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To test the response of a custom error handler, raise the appropriate exception
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in a test view. For example::
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from django.core.exceptions import PermissionDenied
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from django.http import HttpResponse
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from django.test import SimpleTestCase, override_settings
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from django.urls import path
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def response_error_handler(request, exception=None):
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return HttpResponse('Error handler content', status=403)
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def permission_denied_view(request):
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raise PermissionDenied
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urlpatterns = [
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path('403/', permission_denied_view),
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]
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handler403 = response_error_handler
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# ROOT_URLCONF must specify the module that contains handler403 = ...
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@override_settings(ROOT_URLCONF=__name__)
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class CustomErrorHandlerTests(SimpleTestCase):
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def test_handler_renders_template_response(self):
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response = self.client.get('/403/')
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# Make assertions on the response here. For example:
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self.assertContains(response, 'Error handler content', status_code=403)
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