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.
--
Steven
299792.458 km/s — not just a good idea, it’s the law!
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