There is no change to PEP 302. imp.source_from_cache() and

imp.cache_from_source() may return None.

pep-3147.txt

@@ -438,16 +438,9 @@ package [17]_:
 
 Alternative implementations are free to override these functions to
 return reasonable values based on their own support for this PEP.
-
-
-PEP 302 loaders
----------------
-
-PEP 302 [18]_ defined loaders have a `.get_filename()` method which
-points to the `__file__` for a module.  As part of this PEP, we will
-extend this API, to include a new method `.get_paths()` which will
-return a 2-tuple containing the path to the source file and the path
-to where the matching `pyc` file is (or would be).
+These methods are allowed to return `None` when the implementation (or
+PEP 302 loader [18]_ in effect) for whatever reason cannot calculate
+the appropriate file name.  They should not raise exceptions.
 
 
 Backports