[Python-Dev] Draft PEP: "Simplified Package Layout and Partitioning"
pje at telecommunity.com
Wed Jul 20 15:05:47 CEST 2011
At 02:24 AM 7/20/2011 -0700, Glenn Linderman wrote:
>When I read about creating __path__ from sys.path, I immediately
>thought of the issue of programs that extend sys.path, and the above
>is the "workaround" for such programs.Â but it requires such
>programs to do work, and there are a lot of such programs (I, a
>relative newbie, have had to write some).Â As it turns out, I can't
>think of a situation where I have extended sys.path that would
>result in a problem for fancy namespace packages, because so far
>I've only written modules, not packages, and only modules are on the
>paths that I add to sys.path.Â But that does not make for a general solution.
Most programs extend sys.path in order to import things. If those
things aren't yet imported, they don't have a __path__ yet, and so
don't need to be fixed. Only programs that modify sys.path *after*
importing something that has a dynamic __path__ would need to do
anything about that.
>Is there some way to create a new __path__ that would reflect the
>fact that it has been dynamically created, rather than set from
>__init__.py, and then when it is referenced, calculate (and cache?)
>a new value of __path__ to actually search?
That's what extend_virtual_paths() is for. It updates the __path__
of all currently-imported virtual packages. Where before you wrote:
You would now write:
...assuming you have virtual packages you've already imported. If
you don't, there's no reason to call extend_virtual_paths(). But it
doesn't hurt anything if you call it unnecessarily, because it uses
sys.virtual_packages to find out what to update, and if you haven't
imported any virtual packages, there's nothing to update and the call
will be a quick no-op.
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