[Import-SIG] PEP 420: Implicit Namespace Packages

Brett Cannon brett at python.org
Thu Apr 19 23:08:43 CEST 2012

On Thu, Apr 19, 2012 at 16:18, Eric V. Smith <eric at trueblade.com> wrote:

> This reflects (I hope!) the discussions at PyCon. My plan is to produce
> an implementation based on the importlib code, and then flush out pieces
> of the PEP.
> In particular, I want to make sure the PEP addresses the various
> objections that were raised, especially by Nick.

Obviously thanks for writing this up, Eric! I have the following comments
(some of which I would fix myself but I lack hg repo access ATM)  ...

In Terminology, can you put the terms when you define them in quotes, e.g. 'The
term "distribution" refers to ...'?

"setuptools provides a similar function pkg_resources.declare_namespace"
should either have a "named" added in there or a comma.

"As vendors might chose(sic) to".

You should mention that this will do away with the ImportWarning of
discovering a directory lacking an __init__.py file.

As for the effects on path hooks, there are none. =) It's actually the
finders that they return which need to change. Either finders need to be
updated to return something other than None to signal they have a directory
which works for the name (maybe the string for what should go into
__path__?) or another method on finders which is called if
finder.find_module() returns None (like finder.find_namespace() which
returns the directory name or None). Then you need to update
importlib._bootstrap.PathFinder to handle one of the two approaches to
create the module and set it with some __loader__ (which really doesn't
need to do much more than construct a module with the proper attributes
since there is nothing to execute) like
importlib.machinery.NamespaceLoader(name, *paths). Using a specific class
in import already has precedence thanks to NullImporter.

If you want performance then you go with the returning of a string by
finder.find_module() since the finder can keep track of finding a directory
w/o an __init__.py when it tries looking for a module. Import can do a
hasattr check on non-None return values to decide if it got back a loader
or a path for a namespace. If you don't like what the return value to mean
based on it being None or having a specific attribute then you would want
the new method at the (potential) cost of another stat call. Or maybe
someone can think of some other approach.
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