Merge pull request #940 from goodfeli/eval

doc/tutorial/adding.txt

@@ -116,6 +116,31 @@ is a single Variable *or* a list of Variables. For either case, the second
 argument is what we want to see as output when we apply the function. *f* may
 then be used like a normal Python function.
 
+.. note::
+
+    As a shortcut, you can skip step 3, and just use a variable's
+    :func:`eval` method. The :func:`eval` method is not as flexible
+    as :func:`function` but it can do everything we've covered in
+    the tutorial so far. It has the added benefit of not requiring
+    you to import :func:`function` . Here is how :func:`eval` works:
+
+    >>> import theano.tensor as T
+    >>> x = T.dscalar('x')
+    >>> y = T.dscalar('y')
+    >>> z = x + y
+    >>> z.eval({x : 16.3, y : 12.1})
+    array(28.4)
+
+    We passed :func:`eval` a dictionary mapping symbolic theano
+    variables to the values to substitute for them, and it returned
+    the numerical value of the expression.
+
+    :func:`eval` will be slow the first time you call it on a variable--
+    it needs to call :func:`function` to compile the expression behind
+    the scenes. Subsequent calls to :func:`eval` on that same variable
+    will be fast, because the variable caches the compiled function.
+
+
 
 Adding two Matrices
 ===================

theano/gof/graph.py

@@ -405,6 +405,26 @@ class Variable(Node):
                 stacklevel=2)
         del self.fgraph
 
+
+    def eval(self, inputs_to_values = None):
+        """ Evaluates this variable.
+
+        inputs_to_values: a dictionary mapping theano Variables to values.
+        """
+
+        if inputs_to_values is None:
+            inputs_to_values = {}
+
+        if not hasattr(self, '_fn'):
+            self._fn_inputs = inputs_to_values.keys()
+            self._fn = theano.function(self._fn_inputs, self)
+        args = [ inputs_to_values[param] for param in self._fn_inputs ]
+
+        rval = self._fn(*args)
+
+        return rval
+
+
     env = property(env_getter, env_setter, env_deleter)
 
 

theano/gof/tests/test_graph.py

@@ -82,7 +82,7 @@ class X:
         return as_string(inputs, outputs,
                          leaf_formatter = self.leaf_formatter,
                          node_formatter = self.node_formatter)
-    
+
 
 class TestStr(X):
 
@@ -151,7 +151,7 @@ class TestClone(X):
 ############
 
 def prenode(obj):
-    if isinstance(obj, Variable): 
+    if isinstance(obj, Variable):
         if obj.owner:
             return [obj.owner]
     if isinstance(obj, Apply):
@@ -290,3 +290,18 @@ class TestIsSameGraph(unittest.TestCase):
                                     ({y: x, t: z}, True))),
             ],
             debug=False)
+
+
+
+################
+# eval         #
+################
+
+def test_eval():
+    x = tensor.scalar()
+    y = tensor.scalar()
+    z = x + y
+
+    result = z.eval({x : 1., y : 2.})
+
+    assert z == 3.