- copy codes from Sonic.add_route

- modify comment by r0fls

sanic/blueprints.py

@@ -1,6 +1,7 @@
 from collections import defaultdict, namedtuple
 
 from sanic.constants import HTTP_METHODS
+from sanic.views import CompositionView
 
 FutureRoute = namedtuple('Route', ['handler', 'uri', 'methods', 'host'])
 FutureListener = namedtuple('Listener', ['handler', 'uri', 'methods', 'host'])
@@ -86,14 +87,23 @@ class Blueprint:
     def add_route(self, handler, uri, methods=frozenset({'GET'}), host=None):
         """
         Creates a blueprint route from a function.
-        :param handler: Function or class instance to handle uri request.
+        :param handler: Function for handling uri requests. Accepts function, or class instance with a view_class method.
         :param uri: Endpoint at which the route will be accessible.
         :param methods: List of acceptable HTTP methods.
         :return: function or class instance
         """
         # Handle HTTPMethodView differently
         if hasattr(handler, 'view_class'):
-            methods = frozenset(HTTP_METHODS)
+            methods = set()
+
+            for method in HTTP_METHODS:
+                if getattr(handler.view_class, method.lower(), None):
+                    methods.add(method)
+
+        # handle composition view differently
+        if isinstance(handler, CompositionView):
+            methods = handler.handlers.keys()
+
         self.route(uri=uri, methods=methods, host=host)(handler)
         return handler