Steven D'Aprano wrote:
> Suppose I have a library function that reads a global configuration setting:
>
> # Toy example
> SPAMIFY = True
> def make_spam(n):
> if SPAMIFY:
> return "spam"*n
> else:
> return "ham"*n
>
>
> Don't tell me to make SPAMIFY a parameter of the function. I know that.
> That's
> what I would normally do, but *occasionally* it is still useful to have a
> global configuration setting, and those are the cases I'm talking about.
>
>
> Now the caller can say:
>
> import library
> library.SPAMIFY = False
> result = library.make_spam(99)
>
>
> but that would be Wrong and Bad and Evil, because you're affecting *other*
> code, not your code, which relies on SPAMIFY being True. Doing this is
> (maybe)
> okay when testing the library, but not for production use.
>
> What I really want is for make_spam() to be able to look at the caller's
> globals, so that each caller can create their own per-module configuration
> setting:
>
> import library
> SPAMIFY = False # only affects this module, no other modules
> result = library.make_spam(99)
>
>
> But... how can make_spam() look for the caller's globals rather than its own?
>
> I'd rather not do this:
>
>
> def make_spam(n, namespace):
> SPAMIFY = namespace['SPAMIFY']
> ...
>
> which forces the user to do this:
>
> result = library.make_spam(99, globals())
>
>
> which defeats the purpose of making it a global setting. (If I wanted to
> *require* the caller to pass a parameter, I would just force them to pass in
> the flag itself. The whole point is to not require that.)
>
> I'd be okay with making the namespace optional:
>
>
> def make_spam(n, namespace=None):
> if namespace is None:
> namespace = ... # magic to get the caller's globals
> SPAMIFY = namespace['SPAMIFY']
> ...
>
>
> but what magic do I need? globals() is no good, because it returns the
> library's global namespace, not the caller's.
>
>
> Any solution ought to work for CPython, IronPython and Jython, at a minimum.
>
class Library:
SPAMIFY = False
def make_spam(m):
...
import library
Library = library.Library()
result = Library.make_spam(99)
--
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
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