[Python-ideas] 'Injecting' objects as function-local constants
steve at pearwood.info
Tue Jun 14 01:25:52 CEST 2011
Terry Reedy wrote:
> if __name__ == '__main__':
> if '--verbose' in sys.argv:
> wrap = inject(hook=print)
> I do not see the point of all this complication. If you are not trying
> to optimize the function (and adding such hooks is obviously not),
> hook = print
> works just fine (in 3.x ;-).
You're modifying a global variable. Now any other function that calls
do_work() for its own purposes suddenly finds it mysteriously printing.
A classic action-at-a-distance bug. For a simple stand-alone script,
there's no problem, but once you have more complexity in your app, or a
library, things become very different.
My apologies, I've been doing a lot of reading about the pros and cons
(mostly cons *wink*) of monkey-patching in the Ruby world, the
open/closed principle, and various forms of bugs caused by the use of
globals. I assumed that the problems would be blindingly obvious. I
suppose they were only obvious to me because I'd just immersed myself in
them for the last day or so!
More information about the Python-ideas