Change mean() to always return the same dtype even if axis=[].

theano/tensor/basic.py

@@ -3182,6 +3182,9 @@ def mean(input, axis=None, dtype=None, op=False, keepdims=False,
     for i in axis:
         s = true_div(s, shp[i])
 
+    if s.dtype != shp.dtype and s.dtype in discrete_dtypes:
+        s = cast(s, shp.dtype)
+
     if dtype == 'float16' or (dtype is None and input.dtype == 'float16'):
         s = cast(s, 'float16')
     s.name = 'mean'

theano/tensor/tests/test_elemwise.py

@@ -939,7 +939,7 @@ class T_mean_dtype(unittest.TestCase):
             axis = axes[idx % len(axes)]
             x = tensor.matrix(dtype=dtype)
             m = x.mean(axis=axis)
-            if dtype in tensor.discrete_dtypes and axis != []:
+            if dtype in tensor.discrete_dtypes:
                 assert m.dtype == 'float64'
             else:
                 assert m.dtype == dtype, (m, m.dtype, dtype)