James Stroud wrote:
>> I need a magical expanding hash with the following properties:
>>
>> * it creates all intermediate keys
>>
>> meh['foo']['bar] = 1
>>
>> -- works even if meh['foo'] didn't exist before
>>
>> * allows pushing new elements to leaves which are arrays
>>
>> meh['foo']['list] << elem1
>> meh['foo']['list] << elem2
>>
>> * allows incrementing numeric leaves
>>
>> meh['foo']['count'] += 7
>>
>> * serializable
>>
>> I have such a class in ruby. Can python do that?
>>
>
>
> Is this too magical?
>
>
> class meh(dict):
> def __getitem__(self, item):
> if self.has_key(item):
> return dict.__getitem__(self, item)
> else:
> anitem = meh()
> dict.__setitem__(self, item, anitem)
> return anitem
Actually what the OP wants is already a method of dict, it's called
setdefault(). It's not overloaded by "[]" because it's believed to be better to
be able to say "I want auto-generation" explicitally rather than implicitly: it
gives the user more power to control, and to enforce stricter rules.
>>> class meh(dict):
... def __getitem__(self, item):
... return dict.setdefault(self, item, meh())
...
>>> a = meh()
>>> a["foo"]["bar"] = 2
>>> a["foo"]["dup"] = 3
>>> print a["foo"]["bar"]
2
>>> print a
{'foo': {'dup': 3, 'bar': 2}}
So I advise using this class, and suggest the OP to try using setdefault()
explicitally to better understand Python's philosophy.
BTW: remember that setdefault() is written "setdefault()" but it's read
"getorset()".
--
Giovanni Bajo
--
http://mail.python.org/mailman/listinfo/python-list
