For empty list/tuple, use floatX for the dtype instead of the numpy default (float64)

theano/tensor/basic.py

@@ -390,7 +390,8 @@ def constant_or_value(x, rtype, name=None, ndim=None, dtype=None):
             # it will only work if the long fits in int64. For NumPy 1.7.1+,
             # it will work if the long fits in int64 or uint64.
             x_ = numpy.asarray(x)
-
+            if x_.size == 0 and not hasattr(x, 'dtype'):
+                x_ = numpy.asarray(x, dtype=config.floatX)
     assert type(x_) in [numpy.ndarray, numpy.memmap]
 
     bcastable = [d == 1 for d in x_.shape]

theano/tensor/tests/test_basic.py

@@ -7118,6 +7118,16 @@ class T_as_tensor_variable(unittest.TestCase):
         new_inp[...] = inp
         x = as_tensor_variable(new_inp)
 
+    def test_empty_dtype(self):
+        old = theano.config.floatX
+        for dtype in ['float16', 'float32', 'float64']:
+            try:
+                theano.config.floatX = dtype
+                assert theano.tensor.as_tensor_variable(()).dtype == dtype
+                assert theano.tensor.as_tensor_variable([]).dtype == dtype
+            finally:
+                theano.config.floatX = old
+
 
 class test_complex_mod(unittest.TestCase):
     """Make sure % fails on complex numbers."""