[Import-SIG] PEP 420: Implicit Namespace Packages

Eric V. Smith eric at trueblade.com
Fri Apr 20 00:59:56 CEST 2012


On 4/19/2012 5:08 PM, Brett Cannon wrote:

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

Done.

> 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.

Changing finder.find_module() to return a string seems the best thing to do.

Barry and I (and hopefully Jason Coombs) are going to try and get
together and sprint on this in the near future. I might wait to update
the PEP on the affect on finders until we're done.

Thanks again.

Eric.


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