added install_requires dependency on ply
diff --git a/setup.py b/setup.py
index 680d23f..8cc88ac 100644
--- a/setup.py
+++ b/setup.py
@@ -12,6 +12,7 @@
         It parses C code into an AST and can serve as a front-end for

         C compilers or analysis tools.

     """,

+    install_requires=['ply'],

     license='LGPL',

     version='2.02',

     author='Eli Bendersky',