one-time factory in python for an experienced java guy

[Aahz]

In article <23406$4a5c9c7d$d9a2f023$27926 at news.hispeed.ch>,
phonky  <phonky at europe.com> wrote:
>
>import itertools
>
>     class Account(object):
>        def __init__(self, holder, gen=itertools.count()):
>           self.__accountnumber = gen.next()
>
>If you consider my python illiteracy,
>
>"itertools.count(): Make an iterator that returns consecutive integers 
>starting with n"
>
>to me that sounds like that solves the increment issue, but what about
>future modules wanting to plug in a different
>numbering format, e.g. 205434.1234 or whatever?

Here's what I would do:

class Account:
    gen = itertools.count
    gen_instance = None

    def __init__(self, holder):
        if self.gen_instance is None:
            self.__class__.gen_instance = self.gen()
        self._account = self.gen_instance()

Notice that I'm using only a single underscore for ``_account`` to make
inheritance simpler, and I'm using ``self`` to access class attributes
*except* when I need to *set* the class attribute, which requires
``self.__class__``.

Now anyone who wants to change the generator can simply do
module.Account.gen = other_gen 
and it will work as long as no Account() instances have been created (you
don't want the generator to change mid-stream, right?).
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

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