On 2006-10-04, Antoon Pardon <[EMAIL PROTECTED]> wrote:
> On 2006-10-03, LaundroMat <[EMAIL PROTECTED]> wrote:
>> Suppose I have this function:
>>
>> def f(var=1):
>> return var*2
>>
>> What value do I have to pass to f() if I want it to evaluate var to 1?
>> I know that f() will return 2, but what if I absolutely want to pass a
>> value to f()? "None" doesn't seem to work..
>>
>> Thanks in advance.
>>
>
> I think the only general solution for your problem would be to
> define a defaulter function. Something like the following:
>
> Default = object()
>
> def defaulter(f, *args):
>
> while args:
> if args[-1] is Default:
> args = args[:-1]
> else:
> break
> return f(*args)
>
>
> The call:
>
> defaulter(f, arg1, arg2, Default, ..., Default)
>
> would then be equivallent to:
>
> f(arg1, arg2)
>
> Or in your case you would call:
>
> defaulter(f, Default)
A little update, with the functools in python 2.5 you
could turn the above into a decorator. Something like
the following (not tested):
def defaulting(f):
return functools.partial(defaulter, f)
You could then simply write:
@defaulting
def f(var=1):
return var * 2
And for built in or library functions something like:
from itertools import repeat
repeat = defaulting(repeat)
--
Antoon Pardon
--
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