fixed bug where it was possible to make Dimshuffle ops with duplicate output dimensions

theano/tensor/elemwise.py

@@ -101,6 +101,11 @@ class DimShuffle(Op):
         self.new_order = new_order
         self.inplace = inplace
 
+        for i in xrange(len(new_order)-1):
+            j = new_order[i]
+            if j != 'x' and j in new_order[i+1:]:
+                raise ValueError("The same input dimension may not appear twice in the list of output dimensions", (new_order))
+
         # list of dimensions of the input to drop
         self.drop = []
         i2j = {} # this maps i before dropping dimensions to j after dropping dimensions so self.shuffle can be set properly later on

theano/tensor/tests/test_basic.py

@@ -3342,6 +3342,20 @@ def test_unalign():
         if not should_raise:
             raise Exception("Theano raised an exception when none was expected")
 
+def test_dimshuffle_duplicate():
+    x = theano.tensor.vector()
+
+    success = False
+
+    try:
+        y = theano.tensor.DimShuffle((False, ), (0, 0))(x)
+    except ValueError, e:
+        assert str(e).find("may not appear twice") != -1
+        success = True
+
+    assert success
+
+
 if __name__ == '__main__':
     if 1:
         unittest.main()