Explicitly activate compat module

docs/extensions.rst

@@ -33,12 +33,14 @@ depending on how the extension is distributed.
 We recommend importing from ``flask.ext`` even with older versions of
 Flask however.  If you have an application that needs to work with
 versions of Flask older than 0.8 you should activate the
-``flaskext_compat`` module which provides the ``flask.ext`` module.  You
-can download it from github: `flaskext_compat.py`_
+``flaskext_compat`` module which provides the ``flask.ext`` module if
+you activate it.  You can download it from github: `flaskext_compat.py`_
 
-You can use it like this::
+And here is how you can use it::
 
     import flaskext_compat
+    flaskext_compat.activate()
+
     from flask.ext import foo
 
 Once the ``flaskext_compat`` module is imported the :data:`flask.ext` will

scripts/flaskext_compat.py

@@ -14,39 +14,30 @@
     :copyright: (c) 2011 by Armin Ronacher.
     :license: BSD, see LICENSE for more details.
 """
+import sys
+import imp
+
+
+ext_module = imp.new_module('flask.ext')
+ext_module.__path__ = []
+ext_module.__package__ = ext_module.__name__
 
 
 class _ExtensionImporter(object):
-    """This importer redirects imports from this submodule to other locations.
-    This makes it possible to transition from the old flaskext.name to the
-    newer flask_name without people having a hard time.
+    """This importer redirects imports from the flask.ext module to other
+    locations.
     """
     _module_choices = ['flask_%s', 'flaskext.%s']
-
-    def __init__(self):
-        from sys import meta_path
-        self.prefix = __name__ + '.'
-        self.prefix_cutoff = __name__.count('.') + 1
-
-        # since people might reload the flask.ext module (by accident or
-        # intentionally) we have to make sure to not add more than one
-        # import hook.  We can't check class types here either since a new
-        # class will be created on reload.  As a result of that we check
-        # the name of the class and remove stale instances.
-        def _name(x):
-            cls = type(x)
-            return cls.__module__ + '.' + cls.__name__
-        this = _name(self)
-        meta_path[:] = [x for x in meta_path if _name(x) != this] + [self]
+    prefix = ext_module.__name__ + '.'
+    prefix_cutoff = prefix.count('.')
 
     def find_module(self, fullname, path=None):
         if fullname.startswith(self.prefix):
             return self
 
     def load_module(self, fullname):
-        from sys import modules
-        if fullname in modules:
-            return modules[fullname]
+        if fullname in sys.modules:
+            return sys.modules[fullname]
         modname = fullname.split('.', self.prefix_cutoff)[self.prefix_cutoff]
         for path in self._module_choices:
             realname = path % modname
@@ -54,20 +45,17 @@ class _ExtensionImporter(object):
                 __import__(realname)
             except ImportError:
                 continue
-            module = modules[fullname] = modules[realname]
+            module = sys.modules[fullname] = sys.modules[realname]
             if '.' not in modname:
-                setattr(modules[__name__], modname, module)
+                setattr(ext_module, modname, module)
             return module
         raise ImportError(fullname)
 
 
-import sys
-import flask
-try:
-    __import__('flask.ext')
-except ImportError:
-    sys.modules['flask.ext'] = flask.ext = sys.modules[__name__]
-    __name__ = __package__ = 'flask.ext'
-    __path__ = []
-    _ExtensionImporter()
-del _ExtensionImporter, sys, flask
+def activate():
+    """Activates the compatibility system."""
+    import flask
+    if hasattr(flask, 'ext'):
+        return
+    sys.modules['flask.ext'] = flask.ext = ext_module
+    sys.meta_path.append(_ExtensionImporter())