Merge pull request #5196 from Thrandis/ccw

theano/scan_module/scan.py

@@ -449,6 +449,16 @@ def scan(fn,
                              getattr(outs_info[i]['initial'], 'name', 'None'),
                              i)
                 outs_info[i]['taps'] = [-1]
+            elif outs_info[i].get('taps', None) is not None:
+                # Check that taps are valid (< 0 and all dfferent)
+                taps = outs_info[i]['taps']
+                if len(taps) > len(set(taps)):
+                    raise ValueError(('All the taps must be different in '
+                                      ' `outputs_info`'), outs_info[i])
+                for t in taps:
+                    if t >= 0:
+                        raise ValueError(('All the tap values must be '
+                                          'smaller than 0.'), outs_info[i])
         else:
             # if a None is provided as the output info we replace it
             # with an empty OrdereDict() to simplify handling

theano/scan_module/tests/test_scan.py

@@ -5454,3 +5454,15 @@ def test_constant_folding_n_steps():
         theano.function([], res)()
     finally:
         theano.config.on_opt_error = on_opt_error
+
+
+def test_outputs_taps_check():
+    """Checks that errors are raised with bad output_info taps."""
+    x = tensor.fvector('x')
+    y = tensor.fvector('y')
+    f = lambda x, y: [x]
+    outputs_info = {'initial': y, 'taps': [0]}
+    assert_raises(ValueError, theano.scan, f, x, outputs_info)
+    outputs_info = {'initial': y, 'taps': [-1, -1]}
+    assert_raises(ValueError, theano.scan, f, x, outputs_info)
+    print('done')