[Python-ideas] Use __all__ for dir(module) (Was: PEP 562)

[Cody Piersall]

On Sun, Sep 17, 2017 at 9:49 PM, Guido van Rossum <guido at python.org> wrote:
> I ave to agree with the other committers who already spoke up.
>
> I'm not using tab completion much (I have a cranky old Emacs setup), but
> isn't making tab completion better a job for editor authors (or
> language-support-for-editor authors) rather than for the core language? What
> editor are you using that calls dir() for tab completion?
>
>> From my perspective, the big benefit of this change is that
>> tab-completion will get better for libraries which are already
>> defining __all__.  This will make for a better REPL experience.  The
>> only code in the stdlib that broke were tests in test_pkg which were
>> explicitly checking the return value of dir().  Apart from that,
>> nothing broke.

I'm sorry, I should have been more specific here. The tab completion
provided by Jupyter uses dir() to provide the relevant tab-completion
options.  I was motivated to put this PR together whenever someone (I
think Nathaniel Smith) was talking about setting a custom __dir__ on a
module by overriding class, and IIRC his motivation was so that no one
tab-completes to use a deprecated attribute.  I spend a _lot_ of time
in a Jupyter environment, so most of my tab completion is provided by
whatever dir() returns.  I think this is a pretty common setup.

The default REPL also uses dir() for populating the completion list.
Since my only interaction with dir() has to do with tab completion, I
may be unaware of use cases where this PR would actually break working
code.  I understand (and agree with!) the emphasis the Python
developers place on backwards compatibility, but I just can't think of
code that would be broken by this change.  Of course, that doesn't
mean it doesn't exist!

Cody