commit b3b180857bcca0f74100686aa0f2e80b51dca78e
Author: Gregory M. Turner <gmt@be-evil.net>
Date:   Mon Dec 22 13:39:54 2014 -0800

    distutils.command.build_ext: accomodate Extension duck-types
    
    Signed-off-by: Gregory M. Turner <gmt@be-evil.net>

diff --git a/Lib/distutils/command/build_ext.py b/Lib/distutils/command/build_ext.py
index 54ce134..8cee284 100644
--- a/Lib/distutils/command/build_ext.py
+++ b/Lib/distutils/command/build_ext.py
@@ -366,7 +366,8 @@ class build_ext(Command):
                   "'ext_modules' option must be a list of Extension instances")
 
         for i, ext in enumerate(extensions):
-            if isinstance(ext, Extension):
+            # Is it an Extension instance or duck-type thereof?
+            if hasattr(ext, 'define_macros'):
                 continue                # OK! (assume type-checking done
                                         # by Extension constructor)