Better error message when the test_value do not have the right type

theano/gof/op.py

@@ -16,8 +16,10 @@ import inspect
 import logging
 import numpy
 import os
-import sys
 import re
+import StringIO
+import sys
+import traceback
 import warnings
 
 import theano
@@ -448,7 +450,31 @@ class PureOp(object):
             return v.get_value(borrow=True, return_internal_type=True)
         elif isinstance(v, graph.Variable) and hasattr(v.tag, 'test_value'):
             # ensure that the test value is correct
-            return v.type.filter(v.tag.test_value)
+            try:
+                ret = v.type.filter(v.tag.test_value)
+            except Exception, e:
+                # Better error message.
+                detailed_err_msg = (
+                    "For compute_test_value, one input test value do not"
+                    " have the requested type.\n")
+                tr = getattr(v.tag, 'trace', None)
+                if tr:
+                    sio = StringIO.StringIO()
+                    traceback.print_list(tr, sio)
+                    tr = sio.getvalue()
+                    detailed_err_msg += (
+                        " \nBacktrace when that variable is created:\n")
+                    detailed_err_msg += str(tr)
+                detailed_err_msg += (
+                    "\nThe error when converting the test value to that"
+                    " variable type:")
+                # We need to only have 1 args and it should be of type
+                # string.  Otherwise, it print the tuple and so the
+                # new line do not get printed.
+                args = (detailed_err_msg,) + tuple(str(arg) for arg in e.args)
+                e.args = ("\n".join(args),)
+                raise
+            return ret
 
         raise AttributeError('%s has no test value' % v)
 

theano/gof/type.py

@@ -307,8 +307,7 @@ class PureType(object):
     def make_constant(self, value, name=None):
         return self.Constant(type=self, data=value, name=name)
 
-
-    def __call__(self, name = None):
+    def __call__(self, name=None, limit=None):
         """Return a new `Variable` instance of Type `self`.
 
         :Parameters:
@@ -316,7 +315,7 @@ class PureType(object):
             A pretty string for printing and debugging.
 
         """
-        return utils.add_tag_trace(self.make_variable(name))
+        return utils.add_tag_trace(self.make_variable(name), limit=limit)
 
     def values_eq(self, a, b):
         """

theano/gof/utils.py

@@ -50,12 +50,16 @@ if sys.version_info[:2] > (3, 4):
     simple_extract_stack = traceback.extract_stack
 
 
-def add_tag_trace(thing):
+def add_tag_trace(thing, limit=None):
     """Add tag.trace to an node or variable.
 
     The argument is returned after being affected (inplace).
+    :param thing: the object where we add .tag.trace
+    :param limit: The limit of the stack size.
+        If None use, config.traceback.limit
     """
-    limit = config.traceback.limit
+    if limit is None:
+        limit = config.traceback.limit
     if limit == -1:
         limit = None
     tr = simple_extract_stack(limit=limit)[:-1]

theano/tensor/basic.py

@@ -744,7 +744,12 @@ def get_scalar_constant_value(orig_v, elemwise=True):
 
 def tensor(*args, **kwargs):
     name = kwargs.pop('name', None)
-    return TensorType(*args, **kwargs).make_variable(name=name)
+    # This add an indirection to the normal call stack. So raise the
+    # limit to keep the good user line.
+    limit = config.traceback.limit
+    if limit != -1:
+        limit += 1
+    return TensorType(*args, **kwargs)(name=name, limit=limit)
 
 
 def _multi(*fns):