adding __dir__

[gangesmaster]

BPO	1591665
Nosy	@arigo, @birkenfeld, @ncoghlan
Files	demo.py: a little test/demo dir.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/birkenfeld'
closed_at = <Date 2007-03-12.13:18:22.000>
created_at = <Date 2006-11-06.21:52:36.000>
labels = ['interpreter-core']
title = 'adding __dir__'
updated_at = <Date 2007-03-12.13:18:22.000>
user = 'https://bugs.python.org/gangesmaster'

bugs.python.org fields:

activity = <Date 2007-03-12.13:18:22.000>
actor = 'georg.brandl'
assignee = 'georg.brandl'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2006-11-06.21:52:36.000>
creator = 'gangesmaster'
dependencies = []
files = ['7605', '7606']
hgrepos = []
issue_num = 1591665
keywords = ['patch']
message_count = 12.0
messages = ['51325', '51326', '51327', '51328', '51329', '51330', '51331', '51332', '51333', '51334', '51335', '51336']
nosy_count = 5.0
nosy_names = ['nnorwitz', 'arigo', 'georg.brandl', 'ncoghlan', 'gangesmaster']
pr_nums = []
priority = 'high'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1591665'
versions = ['Python 2.6']

[gangesmaster]

in accordance with
http://mail.python.org/pipermail/python-dev/2006-November/069865.html

i've written a patch that allows objects to define their
own introspection mechanisms, by providing __dir__.
with this patch:

• dir() returns the locals. this is done in builtin_dir()
• dir(obj) returns the attributes of obj,
  by invoking PyObject_Dir()
• if obj->ob_type has "__dir__", it is used.
  note that it must return a list!
• otherwise, use default the mechanism of collecting
  attributes
• for module objects, return __dict__.keys()
• for type objects, return __dict__.keys() +
  dir(obj.__base__)
• for all other objects, return __dict__.keys() +
  __members__ + __methods__ + dir(obj.__class__)
• builtin_dir takes care of sorting the list

[ncoghlan]

Logged In: YES
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The retrieval of locals on a NULL argument and the sorting
step need to move back inside PyObject_Dir to avoid changing
the C API.

If the standard library's current C API tests didn't break
on this version of the patch, then the final version of the
patch should include enhanced tests for PyObject_Dir that
pass both before and after the patch is applied to PyObject_Dir.

Other than that, I didn't see any major problems on reading
the code (i.e. refcounts and error handling looked pretty
reasonable). I haven't actually run it though.

[gangesmaster]

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user_id=1406776

okay:

• builtin_dir directly calls PyObject_Dir
• PyObject_Dir handles NULL argument and sorting
• it is now completely compatible with the 2.5 API
• fixed several refcount bugs (i wish we had a tracing gc :)

[nnorwitz]

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user_id=33168

tomer, do you know about configuring with --pydebug? That
helps track down refleaks when running regrtest -R ::.

object.c:
_dir_locals: result is not necessary and locals doesn't
need to be initialized as it's set on the next line. You
could just declare and set it all on one line.

_specialized_dir_type should be static. No need to init
dict. Either don't init result or remove else result =
NULL. I'd prefer removing the else and leaving the init.

_specialized_dir_module should be static. No need to init
dict. Can you get the name of the module and use that in
the error msg: PyModule_GetName()? That would hopefully
provide a nicer error msg.

_generic_dir: No need to init dict.

+ /* XXX api change: how about falling to
obj->ob_type
+ XXX if no __class__ exists? */

Do you mean falling *back*? Also, we've been using
XXX(username): as the format for such comments. So this
would be better as:

/* XXX(tomer): Perhaps fall back to obj->ob_type if no
__class__ exists? */

_dir_object: No need to init dirfunc.

PyObject_Dir: No need to init result.

Are there tests for all conditions? At least:

• dir()
• dir(obj)
• dir(obj_with_no_dict)
• dir(obj_with_no__class__)
• dir(obj_with__methods__)
• dir(obj_with__members__)
• dir(module)
• dir(module_with_no__dict__)
• dir(module_with_invalid__dict__)

There also need to be updates to Doc/lib/libfuncs.tex. If
you can't deal with the markup, just do the best you can in
text and someone else will fixup the markup.

Thanks for attaching the patch as a single file, it's easier
to deal with.

[gangesmaster]

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i like to init all my locals ("just in case"), but
if the rest of the code does not adhere my style,
i'll change that.
anyway, i made the changes to the code, updated the docs,
and added full tests (the original dir() wasn't test
so thoroughly)

-tomer

[birkenfeld]

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user_id=849994

• Instead of doing PyObject_CallFunction(dirfunc, "O", obj)
  you should
  do PyObject_CallFunctionObjArgs(dirfunc, obj, NULL).
• Couldn't __dir__ also be allowed to return a tuple?

[gangesmaster]

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PyObject_CallFunctionObjArgs(dirfunc, obj, NULL)
done

Couldn't __dir__ also be allowed to return a tuple?
no, because tuples are not sortable, and i don't want to
over complicate the c-side code of PyObject_Dir.
having __dir__ returning only a list is equivalent to
__repr__ returning only strings.

[arigo]

Line 20 in demo.py:

assert "__getitem__" in dir(x)

looks strange to me... Foo doesn't inherit from
any sequence or mapping type.

[gangesmaster]

i guess the demo isn't updated/relevant anymore.
instead, concrete tests were added to lib/tests/test_builtin.py