On Thu, Nov 13, 2008 at 11:16 AM, Joe Strout <joe@strout.net wrote:
Static storage is a way of preserving state. Objects are a way of
encapsulating state and behavior. Use an object.
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 '
>
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.c ount=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?
>
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()
>
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.c ount=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?
>
encapsulating state and behavior. Use an object.