Merge pull request #5667 from Thrandis/ccw

theano/gof/fg.py

@@ -7,7 +7,6 @@ types that it can raise.
 from __future__ import absolute_import, print_function, division
 from collections import OrderedDict
 import time
-import traceback
 
 import theano
 from theano.gof import graph
@@ -16,7 +15,6 @@ from theano.gof import toolbox
 from theano import config
 
 from six import iteritems, itervalues
-from six.moves import StringIO
 from theano.gof.utils import get_variable_trace_string
 from theano.misc.ordered_set import OrderedSet
 NullType = None
@@ -52,13 +50,9 @@ class MissingInputError(Exception):
         if kwargs:
             # The call to list is needed for Python 3
             assert list(kwargs.keys()) == ["variable"]
-            tr = getattr(list(kwargs.values())[0].tag, 'trace', [])
-            if isinstance(tr, list) and len(tr) > 0:
-                sio = StringIO()
-                print("\nBacktrace when the variable is created:", file=sio)
-                for subtr in list(kwargs.values())[0].tag.trace:
-                    traceback.print_list(subtr, sio)
-                args = args + (str(sio.getvalue()),)
+            error_msg = get_variable_trace_string(kwargs["variable"])
+            if error_msg:
+                args = args + (error_msg,)
         s = '\n'.join(args)  # Needed to have the new line print correctly
         Exception.__init__(self, s)
 
@@ -393,7 +387,6 @@ class FunctionGraph(utils.object2):
                                      "Theano flag exception_verbosity='high', "
                                      "for more information on this error."
                                      % (node.inputs.index(r), str(node)))
-                        error_msg += get_variable_trace_string(r)
                         raise MissingInputError(error_msg, variable=r)
 
         for node in new_nodes:

theano/scan_module/scan.py

@@ -836,14 +836,21 @@ def scan(fn,
     dummy_outs = outputs
     if condition is not None:
         dummy_outs.append(condition)
-    dummy_f = function(dummy_args,
-                       dummy_outs,
-                       updates=updates,
-                       mode=compile.mode.Mode(linker='py',
-                                              optimizer=None),
-                       on_unused_input='ignore',
-                       profile=False)
-
+    # Perform a try-except to provide a meaningful error message to the
+    # user if inputs of the inner function are missing.
+    try:
+        dummy_f = function(dummy_args,
+                           dummy_outs,
+                           updates=updates,
+                           mode=compile.mode.Mode(linker='py',
+                                                  optimizer=None),
+                           on_unused_input='ignore',
+                           profile=False)
+    except gof.fg.MissingInputError as err:
+        msg = ("\nPlease pass this variable to the scan's inner function. Do "
+               "not forget to also pass it to the `non_sequences` attribute "
+               "of scan.")
+        raise gof.fg.MissingInputError(err.args[0] + msg)
     ##
     # Step 5. Re-arange inputs of scan into a more strict order
     ##

theano/scan_module/tests/test_scan.py

@@ -5518,3 +5518,17 @@ class TestInconsistentBroadcast(unittest.TestCase):
                                  sequences=x,
                                  outputs_info=[dict(initial=initial_x)])
         gs = tensor.grad(y.sum(), x)
+
+
+class TestMissingInputError(unittest.TestCase):
+
+    @raises(theano.gof.fg.MissingInputError)
+    def test_raise_error(self):
+        c = theano.shared(0.)
+        inc = tensor.scalar('inc')
+
+        def count_up():
+            return tensor.zeros(()), {c: c + inc}
+
+        _, updates = theano.scan(count_up, n_steps=20)
+        func = theano.function(inputs=[inc], outputs=[], updates=updates)