Specify import hook support.

pep-0382.txt

@@ -114,6 +114,12 @@ also want to extend __path__). At most one such asterisk gets
 prepended to the path. In addition, the (possibly dotted) names of all
 namespace packages are added to the set sys.namespace_packages.
 
+If the first directory found on the path only contains an __init__.py
+and no \*.pth file, searching the path stops; IOW, namespace packages
+must include at least one .pth file. If both \*.pth files and an
+__init__.py had been found, search continues looking for further
+.pth files.
+
 No other change to the importing mechanism is made; searching modules
 (including __init__.py) will continue to stop at the first module
 encountered. In summary, the process import a package foo works like
@@ -121,13 +127,48 @@ this:
 
  1. sys.path is search for a directory foo, or a file foo.<ext>.
     If a file is found and no directory, it is treated as a module, and imported.
- 2. if it is a directory, it checks for \*.pth files. If it finds
+ 2. if it is a directory, it checks for both \*.pth and an __init__ file. If it finds
-    any, a package is created, and its __path__ is extended.
+    only \*.pth files, a package is created, and its __path__ is extended.
- 3. The __init__ module is imported; this import will search the
+ 3. If neither a \*.pth file nor an __init__.py was found, the
-    __path__ that got computed already.
- 4. If neither a \*.pth file nor an __init__.py was found, the
     directory is skipped, and search for the module/package
-    continues.
+    continues. If an __init__.py was found, further search only looks
+    for \*.pth files.
+ 4. If an __init__ module was found, it is imported, with __path__
+    being initialized to the path computed from the \*.pth files.
+
+Impact on Import Hooks
+----------------------
+
+Both loaders and finders as defined in PEP 302 will need to be changed
+to support namespace packages. Failure to comform to the protocol
+below might cause a package not being recognized as a namespace
+package; loaders and finders not supporting this protocol must raise
+AttributeError when the functions below get accessed.
+
+Finders need to support looking for \*.pth files in step 1 of above
+algorithm. To do so, a finder must support a method:
+
+   finder.find_path(fullname, path=None)
+
+This method will be called in the same manner as find_module, and it
+must return a list of strings, each representing the contents of one
+\*.pth file. If fullname is not found, is not a package, or does not
+have any \*.pth files, None must be returned.
+
+If any \*.pth files are found, but no loader was returned from
+find_module, a package is created and initialized with the path.
+
+If a loader was return, but no \*.pth files, load_module is called
+as defined in PEP 302.
+
+If both \*.pth files where found, and a loader was returned, a new
+method is called on the loader:
+
+   loader.load_module_with_path(load_module, path)
+
+where the path parameter is the list of strings containing the
+contents of all \*.pth files.
+
 
 Discussion
 ==========
@@ -159,6 +200,7 @@ having users and tools starting to special-case 2.7). Prospective
 users of this feature are encouraged to comment on this particular
 question.
 
+
 Copyright
 =========