[Pythonmac-SIG] self-instantiating instances in pyhton
Rayme Jernigan
rayme at pobox.com
Thu Jan 13 21:31:09 CET 2005
You guess right... this is the type of approach I was looking for.
Thanks!!
On Jan 12, 2005, at 7:14 PM, Bob Ippolito wrote:
>
> On Jan 12, 2005, at 12:52, Rayme Jernigan wrote:
>
>> Hi,
>>
>> I'm looking for a language to abuse for a project I'm working on. I
>> know a little Python, but I do not know if it can do this: I'd like
>> to define some class "N" that instantiates objects that can
>> instantiate fresh new objects of that same class... without external
>> controller code.
>>
>> You could use this capability, for example, to generate a red-black
>> tree-type data structure that implicitly instantiates a new node for
>> each new input d1, d2, d3... so on. The algorithm for each node could
>> be:
>>
>> -- Toggle downstream L/R pointer
>> -- If no node there, instantiate one and link to it
>> -- if a node is there, pass the datum to it
>>
>> The execution sequence as the tree builds itself out might look
>> something like this:
>>
>> 1. n0 = N(d0) # new instance of N
>> # (downstream pointer default = "Left")
>> # (the first input data, d0, is instantiated in node n0)
>> # nodes: n0
>>
>> 2. n0.send(d1) # toggle n0's downstream pointer to "Right"
>> # on n0 there is no downstream node right so instantiate a new
>> linked node right n1 with d1
>> # nodes: n0,n1
>>
>> 3. n0. send(d2) # toggle n0's downstream pointer "Left"
>> # in n0 there is no downstream node left so instantiate n2 with d2
>> # nodes: n0,n1,n2
>>
>> 4. n0. send(d3) # toggle n0's downstream pointer "Right"
>> # there exists a downstream node right, n1, so send d3 there
>> # toggle n1's downstream pointer "Right"
>> # in n1 there is no downstream node right so instantiate n3 with d3
>> # nodes: n0,n1,n2,n3
>>
>> 5. n0. send(d4) # toggle n0's downstream pointer "Left"
>> # there exists a downstream node left, n2, so send d4 there
>> # toggle n2's downstream pointer "Right"
>> # in n2 there is no downstream node right so instantiate n4 with d4
>> # nodes: n0,n1,n2,n3,n4
>>
>> 6. n0.send(d5) # toggle n0's downstream pointer "Right"
>> # there exists a downstream node right, n1, so send d5 there
>> # toggle n1's downstream pointer "Left"
>> # in n1 there is no downstream node left so instantiate n5 with d5
>> # nodes: n0,n1,n2,n3,n4,n5
>>
>> 7. n0.send(d6) # So on...
>> # ...
>>
>>
>> Any thoughts about how to do this in Python appreciated. Possible at
>> all? Thanks in advance,
>
> I would guess that you'd want an implementation that looks kinda like
> this:
>
> class RBNode(object):
> def __init__(self, value):
> self.index = 0
> self.nodes = [None, None]
> self.value = value
>
> def send(self, value):
> node = self.nodes[self.index]
> if node is None:
> # use type(self) so that if this is a subclass,
> # then the subclass would be used rather than
> # RBNode
> self.nodes[self.index] = type(self)(value)
> else:
> node.send(value)
> self.index = (self.index + 1) % len(self.nodes)
>
> -bob
>
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