Fixed #12815 -- Added TemplateResponse, a lazy-evaluated Response class. Thanks to Simon Willison for the original idea, and to Mikhail Korobov and Ivan Sagalaev for their assistance, including the draft patch from Mikhail.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14850 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/template/response.py

@@ -0,0 +1,108 @@
+from django.http import HttpResponse
+from django.template import loader, Context, RequestContext
+
+class ContentNotRenderedError(Exception):
+    pass
+
+class SimpleTemplateResponse(HttpResponse):
+
+    def __init__(self, template, context=None, mimetype=None, status=None,
+            content_type=None):
+        # It would seem obvious to call these next two members 'template' and
+        # 'context', but those names are reserved as part of the test Client API.
+        # To avoid the name collision, we use
+        # tricky-to-debug problems
+        self.template_name = template
+        self.context_data = context
+
+        # _is_rendered tracks whether the template and context has been baked into
+        # a final response.
+        self._is_rendered = False
+
+        # content argument doesn't make sense here because it will be replaced
+        # with rendered template so we always pass empty string in order to
+        # prevent errors and provide shorter signature.
+        super(SimpleTemplateResponse, self).__init__('', mimetype, status,
+                                                     content_type)
+
+    def resolve_template(self, template):
+        "Accepts a template object, path-to-template or list of paths"
+        if isinstance(template, (list, tuple)):
+            return loader.select_template(template)
+        elif isinstance(template, basestring):
+            return loader.get_template(template)
+        else:
+            return template
+
+    def resolve_context(self, context):
+        """Convert context data into a full Context object
+        (assuming it isn't already a Context object).
+        """
+        if isinstance(context, Context):
+            return context
+        else:
+            return Context(context)
+
+    @property
+    def rendered_content(self):
+        """Returns the freshly rendered content for the template and context
+        described by the TemplateResponse.
+
+        This *does not* set the final content of the response. To set the
+        response content, you must either call render(), or set the
+        content explicitly using the value of this property.
+        """
+        template = self.resolve_template(self.template_name)
+        context = self.resolve_context(self.context_data)
+        content = template.render(context)
+        return content
+
+    def render(self):
+        """Render (thereby finalizing) the content of the response.
+
+        If the content has already been rendered, this is a no-op.
+
+        Returns the baked response instance.
+        """
+        if not self._is_rendered:
+            self._set_content(self.rendered_content)
+        return self
+
+    is_rendered = property(lambda self: self._is_rendered)
+
+    def __iter__(self):
+        if not self._is_rendered:
+            raise ContentNotRenderedError('The response content must be rendered before it can be iterated over.')
+        return super(SimpleTemplateResponse, self).__iter__()
+
+    def _get_content(self):
+        if not self._is_rendered:
+            raise ContentNotRenderedError('The response content must be rendered before it can be accessed.')
+        return super(SimpleTemplateResponse, self)._get_content()
+
+    def _set_content(self, value):
+        "Overrides rendered content, unless you later call render()"
+        super(SimpleTemplateResponse, self)._set_content(value)
+        self._is_rendered = True
+
+    content = property(_get_content, _set_content)
+
+
+class TemplateResponse(SimpleTemplateResponse):
+    def __init__(self, request, template, context=None, mimetype=None,
+            status=None, content_type=None):
+        # self.request gets over-written by django.test.client.Client - and
+        # unlike context_data and template_name the _request should not
+        # be considered part of the public API.
+        self._request = request
+        super(TemplateResponse, self).__init__(
+            template, context, mimetype, status, content_type)
+
+    def resolve_context(self, context):
+        """Convert context data into a full RequestContext object
+        (assuming it isn't already a Context object).
+        """
+        if isinstance(context, Context):
+            return context
+        else:
+            return RequestContext(self._request, context)