normalize shebang lines to #!/usr/bin/env python
diff --git a/Demo/turtle/tdemo_penrose.py b/Demo/turtle/tdemo_penrose.py
index 4d8a61e..f5824d7 100644
--- a/Demo/turtle/tdemo_penrose.py
+++ b/Demo/turtle/tdemo_penrose.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 """       xturtle-example-suite:
 
           xtx_kites_and_darts.py