Create a PEP 302 importer for managing conditional import of vendored packages from the 'extern' namespace. This technique avoids the use of 'imp' and works even when setuptools is installed as a zipped egg. Ref #229.

--HG--
branch : feature/issue-229

2 files changed, 42 insertions, 45 deletions

diff --git a/setuptools/extern/__init__.py b/setuptools/extern/__init__.py
index e69de29b..803d9e9a 100644
--- a/setuptools/extern/__init__.py
+++ b/setuptools/extern/__init__.py
@@ -0,0 +1,42 @@
+import sys
+
+_VENDORED_NAMES = 'six',
+_SEARCH_PATH = 'setuptools._vendor.', ''
+
+class VendorImporter:
+    """
+    A PEP 302 meta path importer for finding optionally-vendored
+    or otherwise naturally-installed packages from __name__.
+    """
+    def find_module(self, fullname, path=None):
+        root, base, target = fullname.partition(__name__ + '.')
+        if root:
+            return
+        if not any(map(target.startswith, _VENDORED_NAMES)):
+            return
+        return self
+
+    def load_module(self, fullname):
+        root, base, target = fullname.partition(__name__ + '.')
+        for prefix in _SEARCH_PATH:
+            try:
+                __import__(prefix + target)
+                mod = sys.modules[prefix + target]
+                sys.modules[fullname] = mod
+                return mod
+            except ImportError:
+                pass
+        else:
+            raise ImportError(
+                "The '{target}' package is required; "
+                "normally this is bundled with this package so if you get "
+                "this warning, consult the packager of your "
+                "distribution.".format(**locals())
+            )
+
+    @classmethod
+    def install(cls):
+        if not any(isinstance(imp, cls) for imp in sys.meta_path):
+            sys.meta_path.append(cls())
+
+VendorImporter.install()
diff --git a/setuptools/extern/six.py b/setuptools/extern/six.py
deleted file mode 100644
index 6076c208..00000000
--- a/setuptools/extern/six.py
+++ /dev/null
@@ -1,45 +0,0 @@
-"""
-Handle loading a package from system or from the bundled copy
-"""
-
-import imp
-
-
-_SEARCH_PATH = ['setuptools._vendor.six', 'six']
-
-
-def _find_module(name, path=None):
-    """
-    Alternative to `imp.find_module` that can also search in subpackages.
-    """
-
-    parts = name.split('.')
-
-    for part in parts:
-        if path is not None:
-            path = [path]
-
-        fh, path, descr = imp.find_module(part, path)
-
-    return fh, path, descr
-
-
-def _import_in_place(search_path=_SEARCH_PATH):
-    for mod_name in search_path:
-        try:
-            mod_info = _find_module(mod_name)
-        except ImportError:
-            continue
-
-        imp.load_module(__name__, *mod_info)
-        break
-
-    else:
-        raise ImportError(
-            "The '{name}' package is required; "
-            "normally this is bundled with this package so if you get "
-            "this warning, consult the packager of your "
-            "distribution.".format(name=_SEARCH_PATH[-1]))
-
-
-_import_in_place()