diff --git a/pydot.py b/pydot.py
index <HASH>..<HASH> 100644
--- a/pydot.py
+++ b/pydot.py
@@ -1829,8 +1829,9 @@ class Dot(Graph):
           then you may want to give the absolute path to the
           executable (for example, to `dot.exe`) in `prog`.
         """
-        default_names = {'dot', 'twopi', 'neato',
-                         'circo', 'fdp', 'sfdp'}
+        default_names = set([
+            'dot', 'twopi', 'neato',
+            'circo', 'fdp', 'sfdp'])
         if prog is None:
             prog = self.prog
         assert prog is not None
BUG: define set with `set([...])` for python <I>

compatibility, to avoid breaking older code
without significant reason. This change is not
motivated by any other reason.

Support for python < <I> will **not** be
actively maintained.