One thing I miss as I move from REALbasic to Python is the ability to
have static storage within a method -- i.e. storage that is persistent
between calls, but not visible outside the method. I frequently use
this for such things as caching, or for keeping track of how many
objects a factory function has created, and so on.
Today it occurred to me to use a mutable object as the default value
of a parameter. A simple example:
def spam(_count=[0]):
_count[0] += 1
return "spam " * _count[0]
>>> spam()
'spam '
>>> spam()
'spam spam '
This appears to work fine, but it feels a little unclean, having stuff
in the method signature that is only meant for internal use. Naming
the parameter with an underscore "_count" makes me feel a little
better about it. But then, adding something to the module namespace
just for use by one function seems unclean too.
What are your opinions on this idiom? Is there another solution
people generally prefer?
Ooh, for a change I had another thought BEFORE hitting Send rather
than after. Here's another trick:
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?
Best,
- Joe
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