[Tutor] help with refactoring needed -- which approach is morePythonic?

[Kent Johnson]

Brian van den Broek wrote:
> Alan Gauld said unto the world upon 2005-02-10 02:58:
> 
>> Pseudo code:
>>        class Body:
>>           def __init__(self,content):
>>             self.contents = contents
>>             self.nodes = []
>>
>>           def parse(self):
>>              for line in self.contents:
>>                  if line == NodeStartTag:
>>                     node = Node()
>>                  if line == NodeEndTag:
>>                     self.nodes.append(node)
>>                  node.append(line)
>>
>>        class Node:
>>          def __init__(self,lines=[]):
>>               self.lines = lines
>>          def append(self,item):
>>               self.lines.append(item)
>>          def parse(self):
>>               # your parsing method here.
> 
> 
> Hi all,
> 
> YAQ (Yet Another Question):
> 
> Following the general pattern, I end up with a Body object which has an 
> attribute .nodes that consists of a list of Node objects.
> 
> So, something like:
> 
> My Example Body
>    Node List
>       Node the first
>       Node the second
> 
> Is there any way to make methods of the Node class access attributes of 
> `parents' of instances? I would like a Node instance such as Node the 
> first above to be aware just what it is a node of and what its siblings 
> are.

You have to tell it the parent. ("Explicit is better than implicit.") For example you could pass a 
reference to Body to the Node in the constructor:

            def parse(self):
               for line in self.contents:
                   if line == NodeStartTag:
                      node = Node(self)    # HERE
                   if line == NodeEndTag:
                      self.nodes.append(node)
                   node.append(line)

In general I think this is a bad design. I try to avoid telling components about their parents in 
any kind of containment hierarchy. If the component knows about its parent, then the component can't 
be reused in a different context and it can't be tested without creating the expected context.

Is there another way you could accomplish what you want?

Kent

> 
> Does this make sense?
> 
> Best to all,
> 
> Brian vdB
> 
> PS Thanks for the reply to my venting question, Kent.
> 
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