Delete dict and subdict items of some name
Mitya Sirenef
msirenef at lightbird.net
Mon Dec 17 20:09:01 EST 2012
On 12/17/2012 05:00 PM, Dave Angel wrote:
> On 12/17/2012 04:33 PM, Mitya Sirenef wrote:
>> On 12/17/2012 01:30 PM, Tim Chase wrote:
>>> On 12/17/12 11:43, Mitya Sirenef wrote:
>>>> On 12/17/2012 12:27 PM, Gnarlodious wrote:
>>>>> Hello. What I want to do is delete every dictionary key/value
>>>>> of the name 'Favicon' regardless of depth in subdicts, of which
>>>>> there are many. What is the best way to do it?
>>>> Something like this should work:
>>>>
>>>> def delkey(d, key):
>>>> if isinstance(d, dict):
>>>> if key in d: del d[key]
>>>> for val in d.values():
>>>> delkey(val, key)
>>> Unless you have something hatefully recursive like
>>>
>>> d = {}
>>> d["hello"] = d
>>>
>>> :-)
>> True -- didn't think of that..!
>>
>> I guess then adding a check 'if val is not d: delkey(val, key)'
>> would take care of it?
>>
> No, that would only cover the self-recursive case. If there's a dict
> which contains another one, which contains the first, then the recursion
> is indirect, and much harder to check for.
>
> Checking reliably for arbitrary recursion patterns is tricky, but
> do-able. Most people degenerate into just setting an arbitrary max
> depth. But I can describe two approaches to this kind of problem.
>
> 1) build a list of the recursion path at present, and compare against
> the whole path, rather than just the tail. If there are any matches, quit.
>
> 2) make the iterator an object, and instantiate two of them. Then each
> recursive level, iterate the main one once, and the secondary one
> twice. If the two ever match, you have a loop. Deciding what to do at
> that point is tricky because you may have processed some nodes multiple
> times already. But at least it'll terminate, and it doesn't use linear
> memory to do so. I call this one the lollypop algorithm.
>
>
Thanks, this is quite interesting..
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