Improve super() objects support for implicit method calls

[collinwinter]

BPO	1498363
Nosy	@birkenfeld, @rhettinger, @terryjreedy
Files	better_super.patch: Improve super() objects, against r47124

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

Show more details

GitHub fields:

assignee = 'https://github.com/rhettinger'
closed_at = <Date 2010-08-11.19:08:48.712>
created_at = <Date 2006-05-31.17:31:43.000>
labels = ['interpreter-core', 'type-feature']
title = 'Improve super() objects support for implicit method calls'
updated_at = <Date 2011-02-16.07:32:57.166>
user = 'https://bugs.python.org/collinwinter'

bugs.python.org fields:

activity = <Date 2011-02-16.07:32:57.166>
actor = 'orsenthil'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2010-08-11.19:08:48.712>
closer = 'rhettinger'
components = ['Interpreter Core']
creation = <Date 2006-05-31.17:31:43.000>
creator = 'collinwinter'
dependencies = []
files = ['7298']
hgrepos = []
issue_num = 1498363
keywords = []
message_count = 8.0
messages = ['50385', '50386', '50387', '50388', '50389', '110449', '113455', '113613']
nosy_count = 5.0
nosy_names = ['georg.brandl', 'collinwinter', 'rhettinger', 'terry.reedy', 'BreamoreBoy']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'patch review'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue1498363'
versions = ['Python 3.3']

[collinwinter]

The attached patch lets super() objects pass on
implicit __getitem__, __setitem__, __delitem__, __len__
and __hash__ calls. For example, to use len() with
super() objects, one must currently do something like

super(X, X()).__len__()

Likewise for __getitem__,

super(X, X()).__getitem__(item)

That's ugly.

This patch lets these be spelled as

len(super(X, X())) and super(X, X())[item], respectively.

The patch also includes documentation updates and tests
for the new functionality.

The patch was taken against r46582.

[collinwinter]

Logged In: YES
user_id=1344176

The patch has been updated to reflect the current SVN state,
r47124.

[birkenfeld]

Logged In: YES
user_id=849994

Why only these methods? Why not __add__, __call__ etc.?
Implementing all of these methods is a pain and adds
considerable complexity to typeobject.c.

Frankly, I don't see an improvement since you normally only
call super.__getitem__ in __getitem__, and explicit is
better than implicit. Raymond, do you have a second opinion?

[collinwinter]

Logged In: YES
user_id=1344176

I only added these particular methods because they were a)
the only ones I needed at the time, b) the only ones I
really had time to implement. I've now got a few more tuits
freed up, so I'd be happy to implement more of these methods.

As for "explicit is better than implicit", I don't see how
that applies here. The same case could be made for all of
Python's syntax-assisted method calls.

[rhettinger]

At one time, I had explored adding some of these methods and then dropped the idea because it left super() with an odd mish-mash of methods that are 1) forwarded 2) not-supported 3) handled directly by the super-object itself.

For instance, the repr() of a super-object and is handled directly by the super object. Likewise, the members are part of the super-object and not forwarded.

The current state of affairs can be explained (approximately) with the notion that named methods are forwarded but not any of the syntax-assisted implicit calls. This patch clutters that state-of-affairs for a questionable benefit.

If you want to push for this, it should be discussed on python-dev so we can reach a concensus on what super-objects should be expected to do and not do. Is it clear that so.__self__ and repr(so) act on the super object while a call like so[x] will traverse the mro?

Also, if something like this does go in, please optimize the calls to PyString_FromString() to be invoked no more than once per Python session (otherwise, syntax driven implicit calls may end-up being slower than named method access).

[BreamoreBoy]

msg50389 asked for this to be discussed on python-dev. I've searched the archives but didn't find anything obvious. Did I simply miss it or was it never discussed?

[terryjreedy]

I believe this is covered by the PEP-3003 3.2 change moratorium.

[rhettinger]

Am rejecting this feature request because of the concerns mentioned in the post on 4/3. The current requirement for explicit forwarding may be slightly inconvenient to type but it does add provide clarity that the method should be applied to the next-in-mro instead of the super object itself.

I appreciate the idea but think it would complicate an object that is already very difficult to understand and use correctly.