[ python-Feature Requests-925537 ] dir(mod) OK or use vars(mod).keys()?
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Fri Mar 16 07:02:35 CET 2007
Feature Requests item #925537, was opened at 2004-03-29 11:28
Message generated for change (Comment added) made by nnorwitz
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 4
Private: No
Submitted By: Jim Jewett (jimjjewett)
Assigned to: Nobody/Anonymous (nobody)
Summary: dir(mod) OK or use vars(mod).keys()?
Initial Comment:
The documentation on dir() notes that its behavior may
change across releases.
Several library modules use dir(x) in ways that might
break if it changed too much.
Should these be changed to use vars(obj).keys() (and
possibly sort()), or should the note on dir() be removed?
My own preference would just be to provide some
guidance, such as "The output of dir() will always include
all public variables which do not have a magic meaning."
I realize that the standard library itself could be updated
if dir() changes in an uncomfortable way. My real
concern is which spelling to use in my own code. The
library examples suggest a simpler (and clearer) dir(), but
the documentation still says otherwise.
A quick search for modules using dir() showed possible
trouble in at least cgitb, cmd, FCNTL, inspect, optparse,
os, pickle, rlcompleter, SimpleXMLRPCServer, TERMIOS,
tokenize, unittest, and urllib2.
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>Comment By: Neal Norwitz (nnorwitz)
Date: 2007-03-15 23:02
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Has anything happened? Is this still relevant?
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Comment By: Raymond Hettinger (rhettinger)
Date: 2004-05-20 23:05
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One possible change is in the works. Someone, suggested
that dir() starting including the __name__ attribute.
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Comment By: Tim Peters (tim_one)
Date: 2004-03-30 16:51
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Ya, dir() was *intended* to be a convenience for use at the
interactive shell. I expect the only promise Guido wants to
make about it is that it will show him stuff he finds interesting
as Python changes <0.7 wink>.
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Comment By: Martin v. Löwis (loewis)
Date: 2004-03-30 13:09
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Ok, marking it as a feature request then: Explicitly
pointing out that behaviour may change in the future has
usually been done because change in behaviour is
anticipated, or has happened in the past. Giving stronger
guarantees about future versions a feature that is currently
not provided.
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Comment By: Jim Jewett (jimjjewett)
Date: 2004-03-30 07:28
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The ideal fix would be in documentation (and therefore policy).
I want to do something like
import_list = [x for x in dir(other_mod) if wanted(x)]
It happens to work today on my machine, but the
documentation says that dir(x) may return different results in
different releases. This means that I can't safely use it in
released code.
If there were some indication that dir(module) would continue
to return the same names as vars(module).keys(), then I could
use it. If the differences were only in variables not intended
for export, that would also be OK -- but dir does not current
promise this.
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Comment By: Martin v. Löwis (loewis)
Date: 2004-03-29 14:11
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I fail to see a bug. Which specific usage of dir() does not
work as intended?
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Comment By: Jim Jewett (jimjjewett)
Date: 2004-03-29 11:58
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Correction: "The output of dir (module) will always include ..."
The most common use is figuring out what to do with (import
from) a module.
Symmetry suggests the same for a no-argument call or a class
or type object, but object instances do not use their __dict__
for their attributes; the results are already different there.
-jJ
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Comment By: Jim Jewett (jimjjewett)
Date: 2004-03-29 11:39
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If there concern is over attributes that are "public" but don't
exist until called, then most uses of dir and vars are already
broken. An alternative reasonable promise would be
The output of dir(obj) will always include all (public?,
non-magical?) names in vars(obj).keys().
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