add exception for old versions of pydot

theano/printing.py

@@ -952,7 +952,14 @@ def pydotprint(fct, outfile=None,
     if return_image:
         return g.create(prog='dot', format=format)
     else:
-        g.write(outfile, prog='dot', format=format)
+        try:
+            g.write(outfile, prog='dot', format=format)
+        except pd.InvocationException as e:
+            # based on https://github.com/Theano/Theano/issues/2988
+            if map(int, pd.__version__.split(".")) < [1, 0, 28]:
+                raise Exception("Try upgrading pydot version to a newer one")
+            raise
+
         if print_output_file:
             print('The output file is available at', outfile)