[Python-Dev] Add __exports__ to modules

[M.-A. Lemburg]

Ka-Ping Yee wrote:
> 
> On Wed, 10 Jan 2001, Guido van Rossum wrote:
> > Yes -- I came up with the same thought.
> >
> > So here's a plan: somebody please submit a patch that does only one
> > thing: from...import * looks for __all__ and if it exists, imports
> > exactly those names.  No changes to dir(), or anything.
> 
> Please don't use __all__.  At the moment, __all__ is the only way
> to easily tell whether a particular module object really represents
> a package, and the only way to get the list of submodule names.

But __all__ has to be user-defined, so I don't buy that argument.
Note that the only true way to recognize a package is by looking
for an attribute "__path__" since Python adds this for packages
only.
 
> If __all__ is overloaded to also represent exportable symbols in
> modules, these two pieces of information will be impossible (or
> require much ugly hackery) to obtain.

Again, __all__ is not automatically generated, so trusting it
doesn't get you very far. To be able to find subpackages you will
always have to apply some hackery (based on __path__) in order
to be sure. It would be better to add a helper function to
packages to query this kind of information -- the package usually
knows best where to look and what to look for.

Note that __all__ was explicitly invented to be used by
from package import * so I think it is the right choice here.

-- 
Marc-Andre Lemburg
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