made zero check handle sparse types

theano/gradient.py

@@ -787,10 +787,39 @@ def _populate_grad_dict(var_to_node_to_idx,
                         # it's not undefined or disconnected
                         # The only other valid thing it can be is 0
 
-                        is_zero = False
+                        no_constant_value = True
                         try:
                             constant_value = tensor.get_constant_value(term)
-                        except:
+                            no_constant_value = False
+                        except TypeError:
+                            pass
+
+                        extra_msg = ''
+
+                        # The above won't work if it's a sparse type, handle sparse
+                        # types here
+                        if no_constant_value:
+                            if isinstance(term.type, theano.sparse.SparseType):
+                                if term.owner is not None and isinstance(term.owner.op,
+                                        theano.sparse.CSM):
+                                    data = term.owner.inputs[0]
+                                    try:
+                                        constant_value = tensor.get_constant_value(data)
+                                        no_constant_value = False
+                                    except TypeError:
+                                        print theano.printing.min_informative_str(data)
+                                        extra_msg += " It is a CSM, but its data isn't constant."
+                                        pass
+                                else:
+                                    extra_msg += " It is a SparseType but theano doesn't know how"
+                                    extra_msg += " to turn it into a constant."
+                                #end if CSM
+                            else:
+                                extra_msg += " It is not a SparseType."
+                            #end if SparseType
+                        #end if no_constant_value
+
+                        if no_constant_value:
                             msg = "%s.grad returned %s of type %s for input"
                             msg += " %d. This input's only connections to "
                             msg += "the cost through this op are via "
@@ -800,6 +829,7 @@ def _populate_grad_dict(var_to_node_to_idx,
                             msg += "DisconnectedType and theano can't "
                             msg += "simplify it to a constant, so it's not "
                             msg += "verifiably zeros."
+                            msg += extra_msg
 
                             msg = msg % (str(node.op), str(term),
                                     str(type(term)), i)