Added stricter checks to OpFromGraph constructor

theano/compile/builders.py

@@ -35,11 +35,21 @@ class OpFromGraph(gof.Op):
     """
     
     def __init__(self, inputs, outputs, grad_depth = 1, **kwargs):
+        if not isinstance(outputs, list):
+            raise TypeError('outputs must be list', outputs)
+        for i in inputs + outputs:
+            if not isinstance(i, gof.Variable):
+                raise TypeError('inputs and outputs must be Variable instances', i)
+        if 'updates' in kwargs:
+            raise TypeError('updates are not allowed in kwargs')
+        # TODO: the graph may have implicit inputs like Value and SharedVariable instances.
+        #       what impact to they have on the validity of this Op?
         self.fn = function(inputs, outputs, **kwargs)
         self.inputs = inputs
         self.outputs = outputs
         self.input_types = [input.type for input in inputs]
         self.output_types = [output.type for output in outputs]
+
         if grad_depth > 0:
             output_grads = [t() for t in self.output_types]
             gd = G.grad_sources_inputs(zip(self.outputs, output_grads), self.inputs)