static variables

[Steven D'Aprano]

On Wed, 2 Dec 2015 12:16 pm, Erik wrote:

> On 02/12/15 01:02, Steven D'Aprano wrote:
>> On Tue, 1 Dec 2015 08:15 pm, Grobu wrote:
>>> # -------------------------------------------------
>>>   >>> def test(arg=[0]):
>>> ...     print arg[0]
>>> ...     arg[0] += 1
>> Awesome!
> 
> Hideous!
> 
>> using a mutable default as static storage.
> 
> Exposing something a caller can override as a local, static, supposedly
> "private" value is IMHO a tad ... ugly? (*)


Heh, I agree, and as I suggested, it might be good to have an actual
mechanism for static locals. But using a class is no better: your "static
storage" is exposed as an instance attribute, and even if you flag it
private, *somebody* is going to mess with it.

A closure works, but that obfuscates the code:

def make_test():
    arg = [0]
    def test():
        print arg[0]
        arg[0] += 1
    return test

test = make_test()

Or in Python 3:

def make_test():
    arg = 0
    def test():
        nonlocal arg
        print arg
        arg += 1
    return test

test = make_test()


Python has three not-entirely-awful solutions to the problem of static
locals, but no really great or obvious one.



-- 
Steven