Christos Georgiou wrote:
> I haven't followed the complete discussion about once, but I would assume it
> would be used as such:
>
> once <name> = <expression>
>
> that is, always an assignment, with the value stored as a cellvar, perhaps,
> on first execution 0f the code.
>
> Typically I would use it as:
>
> def function(a):
> once pathjoin = os.path.join
> <etc>
In the "name = (once expr)" form I gave, the property of a constant name
that can't be rebound or that of a value that persists across function
call invocations isn't needed. I was trying to separate the different
behaviors cleanly and clearly.
# once as constant assignment and skipped line later.
for n in range(x, 10):
once startcube x**3 # assigns constant value, skips later
print startcube
startcube += 1 # give an exception
So this is the same as "const startcube x**3", except it's ignored if it
is executed again instead of giving an excepton.
Here the constantness property isn't needed.
# once as calc once, use result many times expression.
for n in range(x, 10):
startcube = (once x**3) # calculated once used many
print startcube
startcube += 1 # Ok to do this
I wasn't suggesting which behavior (or combination of) is correct. That
would depend on what problem is meant to solved.
A fourth property of external has been touched on in these threads where
some of the suggestions require doing a calculation on a yet to be
known value. That's usually handled by linkers in other languages and
probably isn't something desired in a dynamic language like Python.
Cheers,
Ron
* I may not be able to reply, do to leaving on a trip. Already should
be gone. ;-)
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