parsing nested unbounded XML fields with ElementTree
Stefan Behnel
stefan_ml at behnel.de
Tue Nov 26 08:20:28 EST 2013
Larry Martell, 26.11.2013 13:23:
> On Tue, Nov 26, 2013 at 2:38 AM, Stefan Behnel wrote:
>> Larry.Martell... at gmail.com, 25.11.2013 23:22:
>>> I have an XML file that has an element called "Node". These can be nested to any depth and the depth of the nesting is not known to me. I need to parse the file and preserve the nesting. For exmaple, if the XML file had:
>>>
>>> <Node Name="A">
>>> <Node Name="B">
>>> <Node Name="C">
>>> <Node Name="D">
>>> <Node Name="E">
>>>
>>> When I'm parsing Node "E" I need to know I'm in A/B/C/D/E. Problem is I don't know how deep this can be. This is the code I have so far:
>>>
>>> nodes = []
>>>
>>> def parseChild(c):
>>> if c.tag == 'Node':
>>> if 'Name' in c.attrib:
>>> nodes.append(c.attrib['Name'])
>>> for c1 in c:
>>> parseChild(c1)
>>> else:
>>> for node in nodes:
>>> print node,
>>> print c.tag
>>>
>>> for parent in tree.getiterator():
>>> for child in parent:
>>> for x in child:
>>> parseChild(x)
>>
>> This seems hugely redundant. tree.getiterator() already returns a recursive
>> iterable, and then, for each nodes in your document, you are running
>> recursively over its entire subtree. Meaning that you'll visit each node as
>> many times as its depth in the tree.
>>
>>
>>> My problem is that I don't know when I'm done with a node and I should
>>> remove a level of nesting. I would think this is a fairly common
>>> situation, but I could not find any examples of parsing a file like
>>> this. Perhaps I'm going about it completely wrong.
>>
>> Your recursive traversal function tells you when you're done. If you drop
>> the getiterator() bit, reaching the end of parseChild() means that you're
>> done with the element and start backing up. So you can simply pass down a
>> list of element names that you append() at the beginning of the function
>> and pop() at the end, i.e. a stack. That list will then always give you the
>> current path from the root node.
>
> Thanks for the reply. How can I remove getiterator()? Then I won't be
> traversing the nodes of the tree. I can't iterate over tree. I am also
> unclear on where to do the pop(). I tried putting it just after the
> recursive call to parseChild() and I tried putting as the very last
> statement in parseChild() - neither one gave the desired result. Can
> you show me in code what you mean?
untested:
nodes = []
def process_subtree(c, path):
name = c.get('Name') if c.tag == 'Node' else None
if name:
path.append(name)
nodes.append('/'.join(path))
for c1 in c:
process_subtree(c1, path)
if name:
path.pop()
process_subtree(tree.getroot(), [])
Stefan
More information about the Python-list
mailing list