[Python-checkins] peps: Require __loader__ and __package__ to be set by loaders.

[brett.cannon]

http://hg.python.org/peps/rev/108e9e328481
changeset:   4316:108e9e328481
user:        Brett Cannon <brett at python.org>
date:        Fri Apr 27 17:41:29 2012 -0400
summary:
  Require __loader__ and __package__ to be set by loaders.

files:
  pep-0302.txt |  40 ++++++++++++++++++----------------------
  1 files changed, 18 insertions(+), 22 deletions(-)


diff --git a/pep-0302.txt b/pep-0302.txt
--- a/pep-0302.txt
+++ b/pep-0302.txt
@@ -273,25 +273,33 @@
       be a list, but may be empty if __path__ has no further
       significance to the importer (more on this later).
 
-    - It should add an __loader__ attribute to the module, set to the
-      loader object.  This is mostly for introspection, but can be used
+    - The __loader__ attribute must be set to the loader object.
+      This is mostly for introspection and reloading, but can be used
       for importer-specific extras, for example getting data associated
       with an importer.
 
+    - The __package__ attribute [10] must be set.
+
     If the module is a Python module (as opposed to a built-in module or
     a dynamically loaded extension), it should execute the module's code
     in the module's global name space (module.__dict__).
 
     Here is a minimal pattern for a load_module() method:
 
+        # Consider using importlib.util.module_for_loader() to handle
+        # most of these details for you.
         def load_module(self, fullname):
-            ispkg, code = self._get_code(fullname)
+            code = self.get_code(fullname)
+            ispkg = self.is_package(fullname)
             mod = sys.modules.setdefault(fullname, imp.new_module(fullname))
             mod.__file__ = "<%s>" % self.__class__.__name__
             mod.__loader__ = self
             if ispkg:
                 mod.__path__ = []
-            exec code in mod.__dict__
+                mod.__package__ = fullname
+            else:
+                mod.__package__ = fullname.rpartition('.')[0]
+            exec(code, mod.__dict__)
             return mod
 
 
@@ -485,24 +493,9 @@
       importer object, zipimport also adds an attribute "__loader__"
       to the module, containing the zipimport object used to load the
       module.  If such an approach is used, it is important that client
-      code takes care not to break if the get_data method (or the
-      __loader__ attribute) is not available, so it is not clear that
-      this approach offers a general answer to the problem.
-
-    Requiring loaders to set the module's __loader__ attribute means
-    that the loader will not get thrown away once the load is complete.
-    This increases memory usage, and stops loaders from being
-    lightweight, "throwaway" objects.  As loader objects are not
-    required to offer any useful functionality (any such functionality,
-    such as the zipimport get_data() method mentioned above, is
-    optional) it is not clear that the __loader__ attribute will be
-    helpful, in practice.
-
-    On the other hand, finder objects are mostly permanent, as they
-    live or are kept alive on sys.meta_path, sys.path_importer_cache, so
-    for a loader to keep a reference to the importer costs us nothing
-    extra.  Whether loaders will ever need to carry so much independent
-    state for this to become a real issue is questionable.
+      code takes care not to break if the get_data method is not available,
+      so it is not clear that this approach offers a general answer to the
+      problem.
 
     It was suggested on python-dev that it would be useful to be able to
     receive a list of available modules from an importer and/or a list
@@ -586,6 +579,9 @@
     [9] PEP 338: Executing modules as scripts
     http://www.python.org/dev/peps/pep-0338/
 
+    [10] PEP 366: Main module explicit relative imports
+    http://www.python.org/dev/peps/pep-0366/
+
 
 Copyright
 

-- 
Repository URL: http://hg.python.org/peps