On Dec 24, 8:24 am, kj <no.em...@please.post> wrote:
> I want to implement a frozen and ordered dict.
>
> I thought I'd implement it as a subclass of collections.OrderedDict
> that prohibits all modifications to the dictionary after it has
> been initialized.
>
> In particular, calling this frozen subclass's update method should,
> in general, trigger an exception ("object is not mutable").
>
> But OrderedDict's functionality *requires* that its __init__ be
> run, and this __init__, in turn, does part of its initialization
> by calling the update method.
>
Rather than trying to identify the caller, I'd do something like:
class FrozenODict(OrderedDict):
def __init__(self, *args, **kwargs):
OrderedDict.__init__(self, *args, **kwargs)
self.update = self._update # init is complete, so override
# update method for this instance
def _update(self, dict2):
raise Exception("object is immutable!!")
After the __init__, calls to the instance's 'update' function will be
mapped to _update. It's essentially overriding the inherited function
on the fly.
Cheers - Chas
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