Fixed a documentation error and implemented template context processors.

flask.py

@@ -130,6 +130,18 @@ def render_template_string(source, **context):
     return current_app.jinja_env.from_string(source).render(context)
 
 
+def _default_template_ctx_processor():
+    """Default template context processor.  Injects `request`,
+    `session` and `g`.
+    """
+    reqctx = _request_ctx_stack.top
+    return dict(
+        request=reqctx.request,
+        session=reqctx.session,
+        g=reqctx.g
+    )
+
+
 class Flask(object):
     """The flask object implements a WSGI application and acts as the central
     object.  It is passed the name of the module or package of the
@@ -216,6 +228,14 @@ class Flask(object):
         #: To register a function here use the :meth:`request_shtdown`
         #: decorator.
         self.request_shutdown_funcs = []
+
+        #: a list of functions that are called without arguments
+        #: to populate the template context.  Each returns a dictionary
+        #: that the template context is updated with.
+        #: To register a function here, use the :meth:`context_processor`
+        #: decorator.
+        self.template_context_processors = [_default_template_ctx_processor]
+
         self.url_map = Map()
 
         if self.static_path is not None:
@@ -248,9 +268,8 @@ class Flask(object):
                         to add extra variables.
         """
         reqctx = _request_ctx_stack.top
-        context['request'] = reqctx.request
-        context['session'] = reqctx.session
-        context['g'] = reqctx.g
+        for func in self.template_context_processors:
+            context.update(func())
 
     def run(self, host='localhost', port=5000, **options):
         """Runs the application on a local development server.  If the
@@ -325,7 +344,7 @@ class Flask(object):
         :param session: the session to be saved (a
                         :class:`~werkzeug.contrib.securecookie.SecureCookie`
                         object)
-        :param request: an instance of :attr:`response_class`
+        :param response: an instance of :attr:`response_class`
         """
         if session is not None:
             session.save_cookie(response, self.session_cookie_name)
@@ -462,6 +481,11 @@ class Flask(object):
         self.request_shutdown_funcs.append(f)
         return f
 
+    def context_processor(self, f):
+        """Registers a template context processor function."""
+        self.template_context_processors.append(f)
+        return f
+
     def match_request(self):
         """Matches the current request against the URL map and also
         stores the endpoint and view arguments on the request object