Merge pull request #992 from rizar/lookup_feedforward

Make Lookup a child of Feedforward

blocks/bricks/lookup.py

@@ -1,13 +1,16 @@
 """Introduces Lookup brick."""
-from blocks.bricks import Initializable
+from blocks.bricks import Initializable, Feedforward
 from blocks.bricks.base import application, lazy
 from blocks.roles import WEIGHT, add_role
 from blocks.utils import check_theano_variable, shared_floatx_nans
 
 
-class LookupTable(Initializable):
+class LookupTable(Initializable, Feedforward):
     """Encapsulates representations of a range of integers.
 
+    This brick can be used to embed integers, e.g. word indices,
+    into a vector space.
+
     Parameters
     ----------
     length : int
@@ -70,3 +73,15 @@ def get_dim(self, name):
         if name == 'indices':
             return 0
         return super(LookupTable, self).get_dim(name)
+
+    @property
+    def input_dim(self):
+        return 0
+
+    @property
+    def output_dim(self):
+        return self.dim
+
+    @output_dim.setter
+    def output_dim(self, dim):
+        self.dim = dim

tests/bricks/test_lookup.py

@@ -26,3 +26,13 @@ def test_lookup_table():
     assert_equal(lt.get_dim(lt.apply.inputs[0]), 0)
     assert_equal(lt.get_dim(lt.apply.outputs[0]), lt.dim)
     assert_raises(ValueError, lt.get_dim, 'random_name')
+
+    # Test feedforward interface
+    assert lt.input_dim == 0
+    assert lt.output_dim == 3
+    lt.output_dim = 4
+    assert lt.output_dim == 4
+
+    def assign_input_dim():
+        lt.input_dim = 11
+    assert_raises(AttributeError, assign_input_dim)