Fix MakeVector.make_node when their is 0 inputs. It was working in the past and was used.

theano/tensor/opt.py

@@ -217,6 +217,7 @@ class MakeVector(T.Op):
 
     This is a simple version of stack() that introduces far less cruft into the graph.
     
+    Should work with 0 inputs.
     """
     def __init__(self, dtype='int64'):
         self.dtype = dtype
@@ -226,7 +227,7 @@ class MakeVector(T.Op):
         return hash(type(self)) ^ hash(self.dtype)
     def make_node(self, *inputs):
         inputs = map(T.as_tensor_variable, inputs)
-        if not all(a.type == inputs[0].type for a in inputs) or inputs[0].dtype != self.dtype:
+        if not all(a.type == inputs[0].type for a in inputs) or (len(inputs)>0 and inputs[0].dtype != self.dtype):
             dtype=theano.scalar.upcast(self.dtype,*[i.dtype for i in inputs])
             #upcast the input to the determined dtype, but don't upcast downcast anything
             assert dtype==self.dtype, "Upcast the input of MakeVector to dtype gived in init without precissino loss only."

theano/tensor/tests/test_opt.py

@@ -1637,17 +1637,19 @@ class T_local_sum_dimshuffle(unittest.TestCase):
     # test_local_sum_prod_dimshuffle (a * b * c)
     # test_local_sum_divprod_dimshuffle ((a * b) / (c * d))
 
-def test_make_vector_upcast():
+def test_make_vector():
     b = T.bscalar()
     i = T.iscalar()
     d = T.dscalar()
     
-    opt.MakeVector(dtype="int8")(b,b)
-    opt.MakeVector(dtype="int32")(i,b)
-    opt.MakeVector(dtype="int32")(b,i)
-    opt.MakeVector(dtype="float64")(b,i)
-    opt.MakeVector(dtype="float64")(b,d)
-    opt.MakeVector(dtype="float64")(d,i)
+    assert opt.MakeVector(dtype="int8")(b,b).dtype=="int8"
+    assert opt.MakeVector(dtype="int32")(i,b).dtype=="int32"
+    assert opt.MakeVector(dtype="int32")(b,i).dtype=="int32"
+    assert opt.MakeVector(dtype="float64")(b,i).dtype=="float64"
+    assert opt.MakeVector(dtype="float64")(b,d).dtype=="float64"
+    assert opt.MakeVector(dtype="float64")(d,i).dtype=="float64"
+    assert opt.MakeVector(dtype="float64")().dtype=="float64"
+    assert opt.MakeVector(dtype="int64")().dtype=="int64"
 
     #should fail
     for (dtype,inputs) in [("int8",(b,i)),