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Re: Delete dict and subdict items of some name

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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..


-- 
Lark's Tongue Guide to Python: http://lightbird.net/larks/

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Delete dict and subdict items of some name Gnarlodious <gnarlodious@gmail.com> - 2012-12-17 09:27 -0800
  Re: Delete dict and subdict items of some name Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-12-17 17:42 +0000
  Re: Delete dict and subdict items of some name Mitya Sirenef <msirenef@lightbird.net> - 2012-12-17 12:43 -0500
  Re: Delete dict and subdict items of some name Paul Rubin <no.email@nospam.invalid> - 2012-12-17 09:48 -0800
  Re: Delete dict and subdict items of some name Dave Angel <d@davea.name> - 2012-12-17 12:50 -0500
  Re: Delete dict and subdict items of some name Tim Chase <python.list@tim.thechases.com> - 2012-12-17 12:30 -0600
  Re: Delete dict and subdict items of some name Mitya Sirenef <msirenef@lightbird.net> - 2012-12-17 16:33 -0500
  Re: Delete dict and subdict items of some name Chris Angelico <rosuav@gmail.com> - 2012-12-18 08:53 +1100
  Re: Delete dict and subdict items of some name Dave Angel <d@davea.name> - 2012-12-17 17:00 -0500
  Re: Delete dict and subdict items of some name MRAB <python@mrabarnett.plus.com> - 2012-12-17 23:08 +0000
  Re: Delete dict and subdict items of some name Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-12-18 00:17 +0000
  Re: Delete dict and subdict items of some name Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-12-18 00:22 +0000
  Re: Delete dict and subdict items of some name Mitya Sirenef <msirenef@lightbird.net> - 2012-12-17 20:09 -0500
  Re: Delete dict and subdict items of some name Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-12-17 23:44 +0000
  Re: Delete dict and subdict items of some name Dave Angel <d@davea.name> - 2012-12-17 21:13 -0500
  Re: Delete dict and subdict items of some name Gnarlodious <gnarlodious@gmail.com> - 2012-12-17 21:30 -0800
    Re: Delete dict and subdict items of some name Hans Mulder <hansmu@xs4all.nl> - 2012-12-18 11:31 +0100
      Re: Delete dict and subdict items of some name Gnarlodious <gnarlodious@gmail.com> - 2012-12-18 07:27 -0800
        Re: Delete dict and subdict items of some name Terry Reedy <tjreedy@udel.edu> - 2012-12-18 11:29 -0500

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