props added to doc/tutorial/using_gpu.txt

doc/tutorial/using_gpu.txt

@@ -688,14 +688,8 @@ Modify and execute to work for a matrix of shape (20, 10).
     import theano.sandbox.cuda as cuda
 
     class PyCUDADoubleOp(theano.Op):
-        def __eq__(self, other):
-            return type(self) == type(other)
 
-        def __hash__(self):
-            return hash(type(self))
-
-        def __str__(self):
-            return self.__class__.__name__
+        __props__ = ()
 
         def make_node(self, inp):
             inp = cuda.basic_ops.gpu_contiguous(