implemented connection_pattern for Shape op

theano/tensor/basic.py

@@ -2095,18 +2095,21 @@ class Shape(Op):
     def infer_shape(self, node, in_shapes):
         return [[len(in_shapes[0])]]
 
+    def connection_pattern(self):
+        #the grad returns the gradient with respect to the
+        #elements of a tensor variable
+        #the elements of the tensor variable do not participate
+        #in the computation of the shape, so they are not really
+        #part of the graph
+        return [False]
+
     def grad(self, inp, grads):
         #the grad returns the gradient with respect to the
         #elements of a tensor variable
         #the elements of the tensor variable do not participate
         #in the computation of the shape, so they are not really
         #part of the graph
-        #we approximate that by returning 0 for their gradient
-        #if we want to be really strict about the disconnected
-        #input error in tensor.grad we might want to make a way
-        #to report that the elements of a variable do not participate
-        #in computing the op's value
-        return [zeros_like(inp[0])]
+        return [None]
 
     def R_op(self, inputs, eval_points):
         return [None]