Merge pull request #510 from delallea/test_value_scan_fix

theano/scan_module/scan_utils.py

@@ -36,7 +36,7 @@ _logger = logging.getLogger('theano.scan_utils')
 def safe_new(x, tag=''):
     """
     Internal function that constructs a new variable from x with the same
-    type, but with a different name ( old name + tag). This function is used
+    type, but with a different name (old name + tag). This function is used
     by gradient, or the R-op to construct new variables for the inputs of
     the inner graph such that there is no interference between the original
     graph and the newly constructed graph.
@@ -58,12 +58,22 @@ def safe_new(x, tag=''):
         try:
             x = tensor.as_tensor_variable(x)
         except TypeError:
-            # This could happend for example for random states, and I really
+            # This could happen for example for random states, and I really
             # want to avoid the convoluted logic that checks for cuda
             # ndarrays
             pass
     nw_x = x.type()
     nw_x.name = nw_name
+    # Preserve test values so that the 'compute_test_value' option can be used.
+    # The test value is deep-copied to ensure there can be no interactions
+    # between test values, due to inplace operations for instance. This may
+    # not be the most efficient memory-wise, though.
+    if theano.config.compute_test_value != 'off':
+        try:
+            nw_x.tag.test_value = copy.deepcopy(gof.op.get_test_value(x))
+        except AttributeError:
+            # This means `x` has no test value.
+            pass
     return nw_x
 
 
@@ -212,9 +222,9 @@ def get_updates_and_outputs(ls):
                 'The return value of your scan lambda expression may only be '
                 'made of lists, tuples, or dictionaries containing Theano '
                 'variables (or `theano.scan_module.until` objects for '
-                'conditions). In particular if you need to use constant values, '
-                'you can use `tensor.constant` to turn them into Theano '
-                'variables.')
+                'conditions). In particular if you need to use constant '
+                'values, you can use `tensor.constant` to turn them into '
+                'Theano variables.')
 
     if is_outputs(ls):
         return None, _list(ls), {}

theano/scan_module/tests/test_scan.py

@@ -3310,3 +3310,26 @@ if __name__ == '__main__':
     print 37
     scan_tst.test_save_mem_store_steps()
     #'''
+
+
+def test_compute_test_value():
+    """
+    Verify that test values can be used with scan.
+    """
+    backup = theano.config.compute_test_value
+    theano.config.compute_test_value = 'raise'
+    try:
+        x = tensor.vector()
+        xv = numpy.ones(3, dtype=theano.config.floatX)
+        x.tag.test_value = xv
+        y = theano.shared(numpy.arange(3, dtype=theano.config.floatX))
+        z, _ = theano.scan(
+                fn=lambda u, v: u + v,
+                sequences=[x, y])
+        assert not _
+        # The gradient computation used to crash before 6af465e.
+        g = tensor.grad(z.sum(), x)
+        #f = theano.function([x], g)
+        #print f(xv)
+    finally:
+        theano.config.compute_test_value = backup