- Bug fix: when a ``repoze.bfg.resource.PackageOverrides`` class was

  instantiated, and the package it was overriding already had a
  ``__loader__`` attribute, it would fail at startup time, even if the
  ``__loader__`` attribute was another PackageOverrides instance.  We
  now replace any ``__loader__`` that is also a PackageOverrides
  instance.  Symptom: ``ConfigurationExecutionError: <type
  'exceptions.TypeError'>: Package <module 'karl.views' from
  '/Users/chrism/projects/osi/bfgenv/src/karl/karl/views/__init__.pyc'>
  already has a __loader__ (probably a module in a zipped egg)``.

3 files changed, 22 insertions, 5 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 61458163c..3a3c39495 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,7 +1,15 @@
 Next release
 ============
 
-- ...
+- Bug fix: when a ``repoze.bfg.resource.PackageOverrides`` class was
+  instantiated, and the package it was overriding already had a
+  ``__loader__`` attribute, it would fail at startup time, even if the
+  ``__loader__`` attribute was another PackageOverrides instance.  We
+  now replace any ``__loader__`` that is also a PackageOverrides
+  instance.  Symptom: ``ConfigurationExecutionError: <type
+  'exceptions.TypeError'>: Package <module 'karl.views' from
+  '/Users/chrism/projects/osi/bfgenv/src/karl/karl/views/__init__.pyc'>
+  already has a __loader__ (probably a module in a zipped egg)``.
 
 1.0a7 (2009-06-30)
 ==================
diff --git a/repoze/bfg/resource.py b/repoze/bfg/resource.py
index 4112925b4..276c52878 100644
--- a/repoze/bfg/resource.py
+++ b/repoze/bfg/resource.py
@@ -50,9 +50,11 @@ class PackageOverrides:
     implements(IPackageOverrides)
     # pkg_resources arg in kw args below for testing
     def __init__(self, package, pkg_resources=pkg_resources):
-        if hasattr(package, '__loader__'):
-            raise TypeError('Package %s already has a __loader__ '
-                            '(probably a module in a zipped egg)' % package)
+        if hasattr(package, '__loader__') and not isinstance(package.__loader__,
+                                                             self.__class__):
+            raise TypeError('Package %s already has a non-%s __loader__ '
+                            '(probably a module in a zipped egg)' %
+                            (package, self.__class__))
         # We register ourselves as a __loader__ *only* to support the
         # setuptools _find_adapter adapter lookup; this class doesn't
         # actually support the PEP 302 loader "API".  This is
diff --git a/repoze/bfg/tests/test_resource.py b/repoze/bfg/tests/test_resource.py
index 9f466b002..5bc1be152 100644
--- a/repoze/bfg/tests/test_resource.py
+++ b/repoze/bfg/tests/test_resource.py
@@ -123,11 +123,18 @@ class TestPackageOverrides(unittest.TestCase):
             pkg_resources = DummyPkgResources()
         return klass(package, pkg_resources=pkg_resources)
 
-    def test_ctor_package_already_has_loader(self):
+    def test_ctor_package_already_has_loader_of_different_type(self):
         package = DummyPackage('package')
         package.__loader__ = True
         self.assertRaises(TypeError, self._makeOne, package)
 
+    def test_ctor_package_already_has_loader_of_same_type(self):
+        dummy_pkg_resources = DummyPkgResources()
+        package = DummyPackage('package')
+        package.__loader__ = self._makeOne(package)
+        po = self._makeOne(package)
+        self.assertEqual(package.__loader__, po)
+
     def test_ctor_sets_loader(self):
         package = DummyPackage('package')
         po = self._makeOne(package)