Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
From: Andriy Kornatskyy <andriy.kornatskyy@live.com>
To: <ian.g.kelly@gmail.com>, "python-list@python.org" <python-list@python.org>
Subject: RE: Lazy Attribute
Date: Fri, 16 Nov 2012 10:50:56 +0300
Importance: Normal
In-Reply-To: <CALwzidnsKKk1w83JX97rZJcTfhcN6QP4o=M_FM8tXxKyQW7fBg@mail.gmail.com>
References: <DUB117-W881D7D74D529D159D8B33F91520@phx.gbl>, <CALwzidnsKKk1w83JX97rZJcTfhcN6QP4o=M_FM8tXxKyQW7fBg@mail.gmail.com>
Content-Type: text/plain; charset="windows-1251"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.3735.1353052323.27098.python-list@python.org>
Lines: 94
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:33416


Ian=2C

Thank you for mentioning about this research=2C really appreciate that.

Thanks.

Andriy Kornatskyy


----------------------------------------
> From: ian.g.kelly@gmail.com
> Date: Thu=2C 15 Nov 2012 15:46:19 -0700
> Subject: Re: Lazy Attribute
> To: python-list@python.org
>
> On Thu=2C Nov 15=2C 2012 at 12:33 PM=2C Andriy Kornatskyy
> <andriy.kornatskyy@live.com> wrote:
> >
> > A lazy attribute is an attribute that is calculated on demand and only =
once.
> >
> > The post below shows how you can use lazy attribute in your Python clas=
s:
> >
> > http://mindref.blogspot.com/2012/11/python-lazy-attribute.html
> >
> > Comments or suggestions are welcome.
>
> I should add that I like the approach you're taking here. Usually
> when I want a lazy property I just make an ordinary property of a
> memoized function call:
>
> def memoize(func):
> cache =3D {}
> @functools.wraps(func)
> def wrapper(*args=2C **kwargs):
> kwset =3D frozenset(kwargs.items())
> try:
> return cache[args=2C kwset]
> except KeyError:
> result =3D cache[args=2C kwset] =3D func(*args=2C **kwargs)
> return result
> return wrapper
>
> class Foo:
> def __init__(self):
> self.times_called =3D 0
>
> @property
> @memoize # Alternatively=2C use functools.lru_cache
> def forty_two(self):
> self.times_called +=3D 1
> return 6 * 9
>
>
> >>> foo =3D Foo()
> >>> foo.times_called
> 0
> >>> foo.forty_two
> 54
> >>> foo.times_called
> 1
> >>> foo.forty_two
> 54
> >>> foo.times_called
> 1
>
>
> Although you don't go into it in the blog entry=2C what I like about
> your approach of replacing the descriptor with an attribute is that=2C
> in addition to being faster=2C it makes it easy to force the object to
> lazily reevaluate the attribute=2C just by deleting it. Using the
> Person example from your blog post:
>
> >>> p =3D Person('John'=2C 'Smith')
> >>> p.display_name
> 'John Smith'
> >>> p.display_name
> 'John Smith'
> >>> p.calls_count
> 1
> >>> p.first_name =3D 'Eliza'
> >>> del p.display_name
> >>> p.display_name
> 'Eliza Smith'
> >>> p.calls_count
> 2
>
> Although in general it's probably better to use some form of reactive
> programming for that.
> --
> http://mail.python.org/mailman/listinfo/python-list
 		 	   		  =