how to scrutch a dict()

John Nagle nagle at animats.com
Fri Oct 22 19:49:52 CEST 2010


On 10/22/2010 6:10 AM, Ethan Furman wrote:
> John Nagle wrote:

>>
>> class nonnulldict(dict) :
>> def __setitem__(self, k, v) :
>> if not (v is None) :
>> dict.__setitem__(self, k, v)
>>
>> That creates a subclass of "dict" which ignores stores of None values.
>> So you never store the unwanted items at all.
>
> It's going to take more work than that...
>
> --> nnd = nonnulldict(spam='eggs', ham=None, parrot=1)
> --> nnd
> {'ham': None, 'parrot': 1, 'spam': 'eggs'}
> --> d['more_hame'] = None
> --> nnd.update(d)
> --> nnd
> {10000:True, 'more_hame':None, 'ham':None, 'parrot':1, 'spam':'eggs'}

    You're right.


class nonnulldict(dict) :
     def __init__(self, **args) :
         dict.__init__(self)
         for k in args :
             self.__setitem__(k, args[k])
     def __setitem__(self, k, v) :
         if not (v is None) :
            dict.__setitem__(self, k, v)


There should also be a copy constructor, so you can convert a dict to a 
nonnulldict, a list or tuple of pairs to a nonnulldict, etc.
But at least this will raise an exception for those cases.

				John Nagle



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