On Nov 13, 2008, at 8:26 PM, Steven D'Aprano wrote:
def spam(_count=[0]):
_count[0] += 1
return "spam " * _count[0]
This is a common trick, often used for things like caching. One major
advantage is that you are exposing the cache as an *optional* part
of the
interface, which makes testing easier. For example, instead of a test
that looks something like this:
cache = get_access_to_secret_cache() # somehow
modify(cache)
result = function(arg)
restore(cache)
assert something_about(result)
you can simple do this:
result = function(arg, _cache=mycache)
assert something_about(result)
That's a very good point. I'd been working under the assumption that
any outside mucking with the cache was a Bad Thing, but for testing,
it can be darned helpful. And this is a very safe form of mucking; it
doesn't actually affect the "real" cache at all, but just substitutes
a temporary one.
Thanks also for pointing out that this is a common trick -- after all
the attacks on the very idea last night, I was wondering if I were off
alone in the woods again.
def spam2():
if not hasattr(spam2,'count'):spam2.count=0 spam2.count += 1
return "spam2 " * spam2.count
This doesn't expose any uncleanliness outside the function at all.
The
drawback is that the name of the function has to appear several times
within itself, so if I rename the function, I have to remember to
change
those references too. But then, if I renamed a function, I'd have to
change all the callers anyway. So maybe this is better. What do
y'all
think?
I've used this myself, but to me it feels more icky than the semi-
private
argument trick above.
Thanks for the feedback.
Best,
- Joe
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