make get_constant_value go throught Subtensor of MakeVector as Subtensor of Join.

theano/tensor/basic.py

@@ -391,6 +391,20 @@ def get_constant_value(v):
                 ret = get_constant_value(ret)
                 #join can cast implicitly its input in some case.
                 return theano._asarray(ret, dtype=v.type.dtype)
+            if (v.owner.inputs[0].owner and
+                isinstance(v.owner.inputs[0].owner.op,
+                           theano.tensor.opt.MakeVector) and
+                # MakeVector normally accept only scalar as input.
+                # We put this check in case there is change in the future
+                all(var.ndim==0 for var in v.owner.inputs[0].owner.inputs)):
+
+                # The index list 'idx_list' should have length one
+                # since joining scalar variables results in a 1D vector.
+                assert len(v.owner.op.idx_list) == 1
+                ret = v.owner.inputs[0].owner.inputs[v.owner.op.idx_list[0]]
+                ret = get_constant_value(ret)
+                #MakeVector can cast implicitly its input in some case.
+                return theano._asarray(ret, dtype=v.type.dtype)
     raise TypeError(v)
 
 

theano/tensor/tests/test_basic.py

@@ -1571,6 +1571,8 @@ class T_Join_and_Split(unittest.TestCase):
         event when the scalar are simple int type.'''
         a = tensor.iscalar('a')
         b = tensor.lscalar('b')
+        #test when the constant is the first element.
+        #The first element is used in a special way
         s = stack(10,a,b, numpy.int8(3))
         f = function([a,b], s)
         val = f(1,2)
@@ -3468,6 +3470,28 @@ def test_dimshuffle_duplicate():
 
     assert success
 
+class T_get_constant_value(unittest.TestCase):
+
+    def test_get_constant_value(self):
+        a = tensor.stack(1,2,3)
+        assert get_constant_value(a[0])==1
+        assert get_constant_value(a[1])==2
+        assert get_constant_value(a[2])==3
+
+        b = tensor.iscalar()
+        a = tensor.stack(b,2,3)
+        self.assertRaises(TypeError, get_constant_value, a[0])
+        assert get_constant_value(a[1])==2
+        assert get_constant_value(a[2])==3
+
+        #For now get_constant_value got throught only MakeVector and Join of scalar.
+        v = tensor.ivector()
+        a = tensor.stack(v,2,3)
+        self.assertRaises(TypeError, get_constant_value, a[0])
+        self.assertRaises(TypeError, get_constant_value, a[1])
+        self.assertRaises(TypeError, get_constant_value, a[2])
+
+
 if __name__ == '__main__':
     if 1:
         unittest.main()