Copy edited new docs in docs/request_response.txt from [4534]

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4538 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/request_response.txt

@@ -433,30 +433,42 @@ types of HTTP responses. Like ``HttpResponse``, these subclasses live in
 ``HttpResponseServerError``
     Acts just like ``HttpResponse`` but uses a 500 status code.
 
-Returning Errors
+Returning errors
 ================
 
-Returning HTTP error codes in Django is easy; there are the
+Returning HTTP error codes in Django is easy. We've already mentioned the
 ``HttpResponseNotFound``, ``HttpResponseForbidden``,
-``HttpResponseServerError``, etc. subclasses mentioned above which, when
-returned by a view, will make the Web server return the corresponding error
-codes (404, 403, 500, ...) and HTTP headers.
+``HttpResponseServerError``, etc., subclasses; just return an instance of one
+of those subclasses instead of a normal ``HttpResponse`` in order to signify
+an error. For example::
+
+    def my_view(request):
+        # ...
+        if foo:
+            return HttpResponseNotFound('<h1>Page not found</h1>')
+        else:
+            return HttpResponse('<h1>Page was found</h1>')
+
+Because 404 errors are by far the most common HTTP error, there's an easier way
+to handle those errors.
 
 The Http404 exception
 ---------------------
-When you return an error such as ``HttpResponseNotFound``, you are responsible
-for returning the error page and everything yourself. Since this extra
-information will normally be fairly uniform across your site and because you
-often want to bail out of the middle of a view with a quick "content not
-found" error, Django provides the ``Http404`` exception. This exception is
-caught by Django and results in the standard error page for your application
-being returned along with a 404 error code (although this behavior can be
-customised, as described below).
 
-Using this exception in your code would look something like::
+When you return an error such as ``HttpResponseNotFound``, you're responsible
+for defining the HTML of the resulting error page::
+
+    return HttpResponseNotFound('<h1>Page not found</h1>')
+
+For convenience, and because it's a good idea to have a consistent 404 error page
+across your site, Django provides an ``Http404`` exception. If you raise
+``Http404`` at any point in a view function, Django will catch it and return the
+standard error page for your application, along with an HTTP error code 404.
+
+Example usage::
 
     from django.http import Http404
-    # ...
+
     def detail(request, poll_id):
         try:
             p = Poll.objects.get(pk=poll_id)
@@ -472,16 +484,24 @@ Customing error views
 ---------------------
 
 The 404 (page not found) view
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-When you raise the ``Http404`` exception, Django will load a special view
-devoted to handling 404 errors. It finds it by looking for the variable
-``handler404``, which is a string in Python dotted syntax -- the same format
-the normal URLconf callbacks use. A 404 view itself has nothing special: It's
-just a normal view.
+When you raise an ``Http404`` exception, Django loads a special view devoted
+to handling 404 errors. By default, it's the view
+``django.views.defaults.page_not_found``, which loads and renders the template
+``404.html``.
 
-You normally won't have to bother with writing 404 views. By default, URLconfs
-contain the following line::
+This means you need to define a ``404.html`` template in your root template
+directory. This template will be used for all 404 errors.
+
+This ``page_not_found`` view should suffice for 99% of Web applications, but if
+you want to override the 404 view, you can specify ``handler404`` in your
+URLconf, like so::
+
+    handler404 = 'mysite.views.my_custom_404_view'
+
+Behind the scenes, Django determines the 404 view by looking for ``handler404``.
+By default, URLconfs contain the following line::
 
     from django.conf.urls.defaults import *
 
@@ -493,16 +513,37 @@ Three things to note about 404 views:
 
     * The 404 view is also called if Django doesn't find a match after checking
       every regular expression in the URLconf.
+
     * If you don't define your own 404 view -- and simply use the default,
       which is recommended -- you still have one obligation: To create a
       ``404.html`` template in the root of your template directory. The default
       404 view will use that template for all 404 errors.
+
     * If ``DEBUG`` is set to ``True`` (in your settings module) then your 404
       view will never be used, and the traceback will be displayed instead.
 
 The 500 (server error) view
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-URLconfs may also define a ``handler500``, which points to a view to call in
-case of server errors. Server errors happen when you have runtime errors in
-view code.
+Similarly, Django executes special-case behavior in the case of runtime errors
+in view code. If a view results in an exception, Django will, by default, call
+the view ``django.views.defaults.server_error``, which loads and renders the
+template ``500.html``.
+
+This means you need to define a ``500.html`` template in your root template
+directory. This template will be used for all server errors.
+
+This ``server_error`` view should suffice for 99% of Web applications, but if
+you want to override the view, you can specify ``handler500`` in your
+URLconf, like so::
+
+    handler500 = 'mysite.views.my_custom_error_view'
+
+Behind the scenes, Django determines the error view by looking for ``handler500``.
+By default, URLconfs contain the following line::
+
+    from django.conf.urls.defaults import *
+
+That takes care of setting ``handler500`` in the current module. As you can see
+in ``django/conf/urls/defaults.py``, ``handler500`` is set to
+``'django.views.defaults.server_error'`` by default.