[Python-ideas] Default arguments in Python - the return - running out of ideas but...

[Arnaud Delobelle]

On 13 May 2009, at 20:18, CTO wrote:
> Why not just push for some decorators that do this to be included in
> stdlib? I see the utility, but not the point of adding extra syntax.
>
>>>> @Runtime
> ... def f(x=a**2+2b+c):
> ...    return x
> ...
>>>> a = 1
>>>> b = 2
>>>> c = 3
>>>> f()
> 8
>
> This seems much more intuitive and useful to me than adding new
> meanings to yield.

This is not possible.

     def f(x=a**2+2*b+c):
	return x

is compiled to something very much like:

     _tmp = x**2+2*b+c
     def f(x=_tmp):
	return x

So it is impossible to find out what expression yields the default  
value of x by just looking at f.  You have to use lambda or use George  
Sakkis' idea of using strings for defaults and evaluating them at call- 
time (but I'm not sure this will work reliably with nested functions).

-- 
Arnaud