added member sum function

theano/tensor/basic.py

@@ -581,6 +581,9 @@ class _tensor_py_operators:
     def __dot__(left, right): return dot(left, right)
     def __rdot__(right, left): return dot(left, right)
 
+    def sum(self, axis=None):
+        return elemwise.Sum(axis)(self)
+    
 
 class TensorResult(Result, _tensor_py_operators):
     """Subclass to add the tensor operators to the basic `Result` class."""