fixed duplicate-update bug in pfunc

theano/compile/pfunc.py

@@ -157,6 +157,9 @@ def pfunc(params, outputs=None, mode=None, updates=[], givens=[], accept_inplace
     for (store_into, update_val) in iter_over_pairs(updates):
         if not isinstance(store_into, SharedVariable):
             raise TypeError('update target must be a SharedVariable', store_into)
+        if store_into in new_updates:
+            raise ValueError('this shared variable already has an update expression',
+                    (store_into, new_updates[store_into]))
         update_val = v_clone(store_into.filter_update(update_val))
         if update_val.type != store_into.type:
             raise TypeError('an update must have the same type as the original shared variable', 

theano/compile/tests/test_pfunc.py

@@ -2,7 +2,7 @@ import numpy
 import unittest
 import copy
 import theano
-from theano.tensor import Tensor, dmatrix, dvector, lscalar
+from theano.tensor import Tensor, dmatrix, dvector, lscalar, dmatrices
 from theano import tensor
 
 from theano.compile.sharedvalue import *
@@ -193,6 +193,11 @@ class Test_pfunc(unittest.TestCase):
         inc_by_y()
         self.failUnless(x.value == 1)
 
+    def test_duplicate_updates(self):
+        x, y = dmatrices('x', 'y')
+        z = shared(numpy.ones((2,3)))
+        self.failUnlessRaises(ValueError, theano.function, [x,y], [z], updates=[(z, z+x+y), (z, z-x)])
+
     def test_givens(self):
         x = shared(0)
         assign = pfunc([], x, givens = {x: 3})