[Python-ideas] 'Injecting' objects as function-local constants

[David Stanek]

On Sat, Jun 11, 2011 at 9:30 AM, Jan Kaliszewski <zuo at chopin.edu.pl> wrote:

>
> == Proposed solutions ==
>
> I see three possibilities:
>
> 1.
> To add a new keyword, e.g. `inject':
>    def do_and_remember(val, verbose=False):
>        inject mem = collections.Counter()
>        ...
> or maybe:
>    def do_and_remember(val, verbose=False):
>        inject collections.Counter() as mem
>        ...
>
> 2. (which personally I would prefer)
> To add `dummy' (or `hidden') keyword arguments, defined after **kwargs
> (and after bare ** if kwargs are not needed; we have already have
> keyword-only arguments after *args or bare *):
>
>    def do_and_remember(val, verbose=False, **, mem=collections.Counter()):
>        ...
>
> do_and_remember(val, False, mem='something') would raise TypeError and
> `mem' shoudn not appear in help() etc. as a function argument.
>
> 3.
> To provide a special decorator, e.g. functools.within:
>    @functools.within(mem=collections.Counter())
>    def do_and_remember(val, verbose=False):
>        ...
>

For these cases I use a class based solution. It's simple and easy to test.


class DoAndRemember:

    def __init__(self):
        self._mem = collections.Counter()

    def __call__(self, val, verbose=False):
        result = do_something(val)
        self.mem[val] += 1
        if verbose:
            print('Done {} times for {!r}'.format(mem[val], val))

do_and_remember = DoAndRemember()


-- 
David
blog: http://www.traceback.org
twitter: http://twitter.com/dstanek
www: http://dstanek.com
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