Made error message more explicit

theano/scan_module/scan_op.py

@@ -154,12 +154,22 @@ class Scan(PureOp):
     def make_node(self, *inputs):
         assert numpy.all(isinstance(i, gof.Variable) for i in inputs)
         # assert dtype is consistent
-        err_msg1 = ('%s %s (index %d) has dtype %s. Slice %s representing '
-                   'this input has dtype %s' )
-
-        err_msg2 = ('Initial state %s (index %d) has dtype %s. The '
-                    'corresponding output of the inner function applied '
-                    'recurrently has dtype %s')
+        err_msg1 = ('When compiling the inner function of scan the '
+                    'following error has been encountered: The '
+                    '%s %s( the entry number %d) has dtype '
+                    '%s. The corresponding slice %s however has'
+                    ' dtype %s. This should never happen, please '
+                    'report to theano-dev mailing list'
+                   )
+        err_msg2 = ('When compiling the inner function of scan the '
+                    'following error has been encountered: The '
+                    'initial state (outputs_info in scan nomenclature)'
+                    'of variable %s (the entry number %d)'
+                    ' has dtype %s, while the result of the'
+                    ' inner function for this output has dtype %s. This '
+                    'could happen if the inner graph of scan results in '
+                    'an upcast or downcast. Please make sure that you use'
+                    'dtypes consistently')
 
         # Flags that indicate which inputs are vectors
 
@@ -174,7 +184,7 @@ class Scan(PureOp):
         # them have the same dtype
         for idx in xrange(self.n_seqs):
             if inputs[1+idx].dtype != self.inputs[idx].dtype:
-                raise ValueError(err_msg1%( 'Sequence'
+                raise ValueError(err_msg1%( 'sequence'
                                        , str(inputs[1+idx])
                                        , idx
                                        , inputs[1+idx].dtype
@@ -194,7 +204,8 @@ class Scan(PureOp):
         while index < end:
             for k in self.tap_array[index-start]:
                 if inputs[index].dtype != self.inputs[index_i].dtype:
-                    raise ValueError(err_msg1%( 'Initial state'
+                    raise ValueError(err_msg1%( 'initial state (outputs_info'
+                                                ' in scan nomenclature) '
                                                , str(inputs[index])
                                                , index
                                                , inputs[index].dtype
@@ -203,7 +214,7 @@ class Scan(PureOp):
                 index_i += 1
             for k in self.mit_mot_out_slices[index-start]:
                 if inputs[index].dtype != self.outputs[index_o].dtype:
-                    raise ValueError(err_msg2%( inputs[index].name
+                    raise ValueError(err_msg2%( str(inputs[index])
                                                , index
                                                , inputs[index].dtype
                                                , self.outputs[index_o].dtype) )