recursive function: use a global or pass a parameter?

Tim jtim.arnold at gmail.com
Fri Jan 16 19:48:41 CET 2015


On Friday, January 16, 2015 at 1:34:51 PM UTC-5, Peter Otten wrote:
>> Tim wrote:
>> 
> Globals are generally bad as they make code non-reentrant; when two calls of 
> the function run simultaneously the data will be messed up.
> 
> I recommend that you use a generator:
> 
> >>> def walk(obj):
> ...     if not hasattr(obj, "keys"):
> ...         return
> ...     if "things" in obj:
> ...         yield obj["things"]
> ...     for v in obj.values():
> ...         yield from walk(v)
> ... 
> >>> d = {'things':1, 'two':{'things':2}}
> >>> set(walk(d))
> {1, 2}
> 
> In Python before 3.3 you have to replace
> 
> yield from walk(v)
> 
> with a loop:
> 
> for t in walk(v):
>     yield t

Ah, a generator, I wouldn't have seen the problem in this way, but with your example, it looks so natural.

thanks,
--Tim



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