Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
MIME-Version: 1.0
In-Reply-To: <CAMjeLr_PGfGv_uYbuH6Li77bFG-5FCi9GEiLevqjrfAD5SDbAA@mail.gmail.com>
References: <l7t00b$hp7$1@ger.gmane.org> <l7tu0b$s3o$1@ger.gmane.org> <mailman.3748.1386546562.18130.python-list@python.org> <l833rs$jik$1@dont-email.me> <mailman.3752.1386553439.18130.python-list@python.org> <52a52b98$0$2762$c3e8da3$76491128@news.astraweb.com> <CAMjeLr_PGfGv_uYbuH6Li77bFG-5FCi9GEiLevqjrfAD5SDbAA@mail.gmail.com>
Date: Mon, 9 Dec 2013 13:57:28 +1100
Subject: Re: interactive help on the base object
From: Chris Angelico <rosuav@gmail.com>
Cc: Python List <python-list@python.org>
Content-Type: text/plain; charset=UTF-8
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.3755.1386557858.18130.python-list@python.org>
Lines: 55
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:61349

On Mon, Dec 9, 2013 at 1:41 PM, Mark Janssen <dreamingforward@gmail.com> wrote:
>>> What methods, if any does it provide?  Are they all abstract? etc???
>>
>> Pretty much nothing useful :-)
>>
>> py> dir(object)
>> [...]
>>
>
> So (prodding the student), Why does everything inherit from Object if
> it provides no functionality?
>
> Practicality-beats-purity-yours?

Nothing useful to call directly. An int has some useful methods in Python:

>>> (258).to_bytes(2,"little")
b'\x02\x01'

So does a list:

>>> [1,4,1,5,9].count(1)
2

But there's nothing you'd normally want to call from object itself
(except maybe __repr__). There *are*, however, important pieces of
default functionality. Steven mentioned __eq__, and there's also its
pair __hash__. The default system works because the root type provides
implementations of those two functions:

>>> a = object()
>>> b = object()
>>> a == b
False
>>> d = {a:"A", b:"B"}
>>> d[a]
'A'

And it's important that these sorts of things work, because otherwise
a simple Python class would look like this:

class Foo:
    def __new__(self): pass
    def __init__(self): pass
    def __hash__(self): return id(self)
    def __eq__(self, other): return self is other
    # ...

This repetition is exactly what inheritance is good at solving.
Therefore putting that functionality into a base class makes sense;
and since everything MUST have these functions to be able to be used
plausibly, putting them in the lowest base class of all makes the most
sense.

ChrisA