Move monkey patch to a separate module

setuptools/extension.py

@@ -4,63 +4,13 @@ import functools
 import distutils.core
 import distutils.errors
 import distutils.extension
-import distutils.msvc9compiler
 
-from setuptools.dist import _get_unpatched
+from .dist import _get_unpatched
+from . import msvc9_support
 
 _Extension = _get_unpatched(distutils.core.Extension)
 
-def _patch_msvc9compiler_find_vcvarsall():
-    """
-    Looks for the standalone VC for Python before falling back on
-    distutils's original approach.
-    """
-    VC_BASE = r'Software\%sMicrosoft\DevDiv\VCForPython\%0.1f'
-    find_vcvarsall = distutils.msvc9compiler.find_vcvarsall
-    query_vcvarsall = distutils.msvc9compiler.query_vcvarsall
-    if find_vcvarsall and find_vcvarsall.__module__.startswith('setuptools.'):
-        # Already patched
-        return
-
-    def _find_vcvarsall(version):
-        Reg = distutils.msvc9compiler.Reg
-        try:
-            # Per-user installs register the compiler path here
-            productdir = Reg.get_value(VC_BASE % ('', version), "installdir")
-        except KeyError:
-            try:
-                # All-user installs on a 64-bit system register here
-                productdir = Reg.get_value(VC_BASE % ('Wow6432Node\\', version), "installdir")
-            except KeyError:
-                productdir = None
-
-        if productdir:
-            import os
-            vcvarsall = os.path.join(productdir, "vcvarsall.bat")
-            if os.path.isfile(vcvarsall):
-                return vcvarsall
-
-        return find_vcvarsall(version)
-
-    def _query_vcvarsall(version, *args, **kwargs):
-        try:
-            return query_vcvarsall(version, *args, **kwargs)
-        except distutils.errors.DistutilsPlatformError:
-            exc = sys.exc_info()[1]
-            if exc and "vcvarsall.bat" in exc.args[0]:
-                message = 'Microsoft Visual C++ %0.1f is required (%s).' % (version, exc.args[0])
-                if int(version) == 9:
-                    # This redirection link is maintained by Microsoft.
-                    # Contact vspython@microsoft.com if it needs updating.
-                    raise distutils.errors.DistutilsPlatformError(
-                        message + ' Get it from http://aka.ms/vcpython27'
-                    )
-                raise distutils.errors.DistutilsPlatformError(message)
-            raise
-
-    distutils.msvc9compiler.find_vcvarsall = _find_vcvarsall
-    distutils.msvc9compiler.query_vcvarsall = _query_vcvarsall
-_patch_msvc9compiler_find_vcvarsall()
+msvc9_support.patch_for_specialized_compiler()
 
 def have_pyrex():
     """

setuptools/msvc9_support.py

+import sys
+
+import distutils.msvc9compiler
+
+def patch_for_specialized_compiler():
+    """
+    Patch functions in distutils.msvc9compiler to use the standalone compiler
+    build for Python (Windows only). Fall back to original behavior when the
+    standalone compiler is not available.
+    """
+    VC_BASE = r'Software\%sMicrosoft\DevDiv\VCForPython\%0.1f'
+    find_vcvarsall = distutils.msvc9compiler.find_vcvarsall
+    query_vcvarsall = distutils.msvc9compiler.query_vcvarsall
+    if find_vcvarsall and find_vcvarsall.__module__.startswith('setuptools.'):
+        # Already patched
+        return
+
+    def _find_vcvarsall(version):
+        Reg = distutils.msvc9compiler.Reg
+        try:
+            # Per-user installs register the compiler path here
+            productdir = Reg.get_value(VC_BASE % ('', version), "installdir")
+        except KeyError:
+            try:
+                # All-user installs on a 64-bit system register here
+                productdir = Reg.get_value(VC_BASE % ('Wow6432Node\\', version), "installdir")
+            except KeyError:
+                productdir = None
+
+        if productdir:
+            import os
+            vcvarsall = os.path.join(productdir, "vcvarsall.bat")
+            if os.path.isfile(vcvarsall):
+                return vcvarsall
+
+        return find_vcvarsall(version)
+
+    def _query_vcvarsall(version, *args, **kwargs):
+        try:
+            return query_vcvarsall(version, *args, **kwargs)
+        except distutils.errors.DistutilsPlatformError:
+            exc = sys.exc_info()[1]
+            if exc and "vcvarsall.bat" in exc.args[0]:
+                message = 'Microsoft Visual C++ %0.1f is required (%s).' % (version, exc.args[0])
+                if int(version) == 9:
+                    # This redirection link is maintained by Microsoft.
+                    # Contact vspython@microsoft.com if it needs updating.
+                    raise distutils.errors.DistutilsPlatformError(
+                        message + ' Get it from http://aka.ms/vcpython27'
+                    )
+                raise distutils.errors.DistutilsPlatformError(message)
+            raise
+
+    distutils.msvc9compiler.find_vcvarsall = _find_vcvarsall
+    distutils.msvc9compiler.query_vcvarsall = _query_vcvarsall