[CRASH]Fix pydotprint with scan_graphs=True when printing the variables

theano/printing.py

@@ -1018,7 +1018,11 @@ def pydotprint(fct, outfile=None,
             else:
                 new_name = basename + '_' + str(idx)
             new_name = os.path.join(path, new_name + ext)
-            pydotprint(scan_op.op.fn, new_name, compact, format, with_ids,
+            if hasattr(scan_op.op, 'fn'):
+                to_print = scan_op.op.fn
+            else:
+                to_print = scan_op.op.outputs
+            pydotprint(to_print, new_name, compact, format, with_ids,
                        high_contrast, cond_highlight, colorCodes,
                        max_label_size, scan_graphs)
 

theano/tests/test_printing.py

@@ -722,3 +722,24 @@ def test_scan_debugprint5():
 
     for truth, out in zip(expected_output.split("\n"), lines):
         assert truth.strip() == out.strip()
+
+
+def test_printing_scan():
+    def f_pow2(x_tm1):
+        return 2 * x_tm1
+
+    state = theano.tensor.scalar('state')
+    n_steps = theano.tensor.iscalar('nsteps')
+    output, updates = theano.scan(f_pow2,
+                                  [],
+                                  state,
+                                  [],
+                                  n_steps=n_steps,
+                                  truncate_gradient=-1,
+                                  go_backwards=False)
+    f = theano.function([state, n_steps],
+                        output,
+                        updates=updates,
+                        allow_input_downcast=True)
+    theano.printing.pydotprint(output, scan_graphs=True)
+    theano.printing.pydotprint(f, scan_graphs=True)