Ian, Thank you for mentioning about this research, really appreciate that.
Thanks. Andriy Kornatskyy ---------------------------------------- > From: ian.g.ke...@gmail.com > Date: Thu, 15 Nov 2012 15:46:19 -0700 > Subject: Re: Lazy Attribute > To: python-list@python.org > > On Thu, Nov 15, 2012 at 12:33 PM, Andriy Kornatskyy > <andriy.kornats...@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 class: > > > > 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 = {} > @functools.wraps(func) > def wrapper(*args, **kwargs): > kwset = frozenset(kwargs.items()) > try: > return cache[args, kwset] > except KeyError: > result = cache[args, kwset] = func(*args, **kwargs) > return result > return wrapper > > class Foo: > def __init__(self): > self.times_called = 0 > > @property > @memoize # Alternatively, use functools.lru_cache > def forty_two(self): > self.times_called += 1 > return 6 * 9 > > > >>> foo = 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, what I like about > your approach of replacing the descriptor with an attribute is that, > in addition to being faster, it makes it easy to force the object to > lazily reevaluate the attribute, just by deleting it. Using the > Person example from your blog post: > > >>> p = Person('John', 'Smith') > >>> p.display_name > 'John Smith' > >>> p.display_name > 'John Smith' > >>> p.calls_count > 1 > >>> p.first_name = '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 -- http://mail.python.org/mailman/listinfo/python-list
