1 files changed, 31 insertions, 25 deletions
diff --git a/setuptools/extension.py b/setuptools/extension.py
index 980ee0a7..eb8b836c 100644
--- a/setuptools/extension.py
+++ b/setuptools/extension.py
@@ -1,40 +1,46 @@
-from distutils.core import Extension as _Extension
+import sys
+import distutils.core
+import distutils.extension
+
 from setuptools.dist import _get_unpatched
-_Extension = _get_unpatched(_Extension)
 
-# Prefer Cython to Pyrex
-pyrex_impls = 'Cython.Distutils.build_ext', 'Pyrex.Distutils.build_ext'
-for pyrex_impl in pyrex_impls:
-	try:
-		# from (pyrex_impl) import build_ext
-		build_ext = __import__(pyrex_impl, fromlist=['build_ext']).build_ext
-		break
-	except:
-		pass
-have_pyrex = 'build_ext' in globals()
+_Extension = _get_unpatched(distutils.core.Extension)
+
+def have_pyrex():
+    """
+    Return True if Cython or Pyrex can be imported.
+    """
+    pyrex_impls = 'Cython.Distutils.build_ext', 'Pyrex.Distutils.build_ext'
+    for pyrex_impl in pyrex_impls:
+        try:
+            # from (pyrex_impl) import build_ext
+            __import__(pyrex_impl, fromlist=['build_ext']).build_ext
+            return True
+        except Exception:
+            pass
+    return False
 
 
 class Extension(_Extension):
     """Extension that uses '.c' files in place of '.pyx' files"""
 
-    if not have_pyrex:
-        # convert .pyx extensions to .c 
-        def __init__(self,*args,**kw):
-            _Extension.__init__(self,*args,**kw)
-            sources = []
-            for s in self.sources:
-                if s.endswith('.pyx'):
-                    sources.append(s[:-3]+'c')
-                else:
-                    sources.append(s)
-            self.sources = sources
+    def __init__(self, *args, **kw):
+        _Extension.__init__(self, *args, **kw)
+        if not have_pyrex():
+            self._convert_pyx_sources_to_c()
+
+    def _convert_pyx_sources_to_c(self):
+        "convert .pyx extensions to .c"
+        def pyx_to_c(source):
+            if source.endswith('.pyx'):
+                source = source[:-4] + '.c'
+            return source
+        self.sources = map(pyx_to_c, self.sources)
 
 class Library(Extension):
     """Just like a regular Extension, but built as a library instead"""
 
-import sys, distutils.core, distutils.extension
 distutils.core.Extension = Extension
 distutils.extension.Extension = Extension
 if 'distutils.command.build_ext' in sys.modules:
     sys.modules['distutils.command.build_ext'].Extension = Extension
-