Question

I’ve got a function to return a list from an etree element, but it doesn’t look through nested elements.

<elem>
    <variable id="getthis">
        <!-- / -->
    </variable>
    <if>
        <variable id="alsoGetThis">
            <!-- Keep looping through all elements -->
        </variable>
    </if>
</elem>

(I’m working with Valid XML)

So currently the variable within the <if> is ignored, so how can you loop through all levels of the tree? I’m assuming this is a simple task, but maybe I’m wrong. (I’m new to Python & don’t always think like a programmer)

Python func to get the variables:

def collect_vars(self, elem):
    elemVars = []
    if elem.tag == 'variable':
        elemVars.append(elem.attrib['id'])
    elif e in elem == 'variable': # don't want to be doing these
        elemVars.append(e.attrib['id'])
    return elemVars

So all I want to end up with is the list elemVars containing all the variable IDs within the given <elem>

Answer 1

The problem you are facing is that you are not visiting all nodes in the file. You are only visiting the children of the elem element, but you are not visiting the children of these elements. To illustrate this, running the following (I have edited your XML to be valid):

from xml.etree.ElementTree as etree

xml_string = """<elem>
    <variable id="getthis" />
    <if>
        <variable id="alsoGetThis" />
    </if>
    </elem>"""

e = etree.fromstring(xml_string)

for node in e:
    print node

results in

<Element variable at 7f53fbdf1cb0>
<Element if at 7f53fbdf1cf8>

So you are not visiting the child variable of the node if. You will need to recursively visit each node in your XML file, i.e. you function collect_vars will need to call itself. I’ll post some code in a bit to illustrate this.

Edit: As promised, some code to get all id attributes from your element tree. Rather than using an accumulator as Niek de Klein has I have used a generator. This has a number of advantages. For example, this returns the ids one at a time, so you can stop processing at any point, if, for example, a certain id is encountered, which saves reading the entire XML file.

def get_attrs(element, tag, attr):
    """Return attribute `attr` of `tag` child elements of `element`."""

    # If an element has any cildren (nested elements) loop through them:
    if len(element):
         for node in element:
            # Recursively call this function, yielding each result:
            for attribute in get_attrs(node, tag, attr):
                yield attribute

    # Otherwise, check if element is of type `tag` with attribute `attr`, if so
    # yield the value of that attribute.
    if element.tag == 'variable':
        if attr in element.attrib:
            yield element.attrib[attr]

ids = [id for id in get_attrs(e, 'variable', 'id')]

print ids

This yields the result

 ['getthis', 'alsoGetThis']