docstring and test for setdefault, fixes #427

theano/tensor/basic.py

@@ -1397,8 +1397,15 @@ class Repeat(gof.Op):
 repeat = Repeat()
 
 class SetDefault(gof.Op):
-    view_map = {0: [1]}
+    """
+    Takes an input x and a default value. If the input is not None, a
+    reference to it is returned. If the input is None, a copy of the
+    default value is returned instead. The input and the default must
+    have exactly the same type.
+    """
+    view_map = {0: [0]}
     def make_node(self, x, default):
+        x, default = as_tensor_variable(x), as_tensor_variable(default)
         assert x.type == default.type
         return gof.Apply(self, [x, default], [default.type()])
     def perform(self, node, (x, default), (out, )):

theano/tensor/tests/test_basic.py

@@ -1956,8 +1956,24 @@ def test_convert_to_complex():
             b = value(numpy.ones(3, dtype='complex64'))
             f = function([a],basic.convert_to_complex64(a))
             assert a.type.values_eq_approx(b.data, f(a.data))
-      
 
+def test_setdefault():
+    x, y = dscalars('xy')
+    z = setdefault(x, y)
+    f = function([x, y], z)
+    assert f(1, 2) == 1
+    assert f(None, 2) == 2
+    assert f(1, None) == 1
+
+def test_setdefault_state():
+    x, y = dscalars('xy')
+    z = setdefault(x, 3.8)
+    new_x = y + z
+    f = function([y, compile.In(x, update = new_x, value = 12.0)], new_x)
+    assert f(3) == 15
+    f['x'] = None
+    assert f(1) == 4.8
+    assert f(2.2) == 7
     
 def test_bug_complext_10_august_09():
     v0 = dmatrix()