Merge pull request #869 from pascanur/fix_sandbox_scan

theano/sandbox/scan.py

@@ -262,7 +262,9 @@ def scan(fn,
         # makes code much cleaner for those who do not use taps. Otherwise
         # they would always had to shape_padleft the initial state ..
         # which is ugly
-        if init_out['taps'] == [-1]:
+
+        # Note, 'taps' might not be in the dictionary
+        if 'taps' in init_out and init_out['taps'] == [-1]:
 
             actual_arg = init_out['membuf']
             arg = safe_new(init_out['membuf'][0])

theano/sandbox/test_scan.py

@@ -62,10 +62,22 @@ def test_004():
     val_sq = numpy.float32([1,2,3,4,5])
     assert numpy.all(fn(val_sq, 5) == val_sq +1)
 
+def test_005():
+    sq = theano.tensor.fvector('sq')
+    nst = theano.tensor.iscalar('nst')
+    out, _ = scan.scan(lambda s: s+numpy.float32(1),
+                       sequences=sq,
+                       states = [None],
+                       n_steps = nst)
+    fn = theano.function([sq, nst], out)
+    val_sq = numpy.float32([1,2,3,4,5])
+    assert numpy.all(fn(val_sq, 5) == val_sq +1)
+
 
 if __name__=='__main__':
     test_001()
     test_002()
     test_003()
     test_004()
+    test_005()