Tim wrote:
> I have this type of situation and wonder if I should use a global variable
> outside the recursive function instead of passing the updated parameter
> through.
>
> I want to get a union of all the values that any 'things' key may have,
> even in a nested dictionary (and I do not know beforehand how deep the
> nesting might go):
>
> d = {'things':1, 'two':{'things':2}}
>
> def walk(obj, res):
> if not hasattr(obj, 'keys'):
> return set(), set()
>
> if 'things' in obj:
> res.add(obj['things'])
>
> for k in obj:
> walk(obj[k], res)
>
> return res
>
> walk(d, set()) # returns {1, 2}
>
> Is it better to use a global to keep track of the values or does it even
> matter?
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
--
https://mail.python.org/mailman/listinfo/python-list
