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May 5th, 2009

Iterating and removing an element from ElementTree

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Hi. I have an xml file like this:

xml Syntax (Toggle Plain Text)
<tree>
    <category title="Item 1">item 1 text
        <subitem title="subitem1">subitem1 text</fileitem>
        <subitem title="subitem2">subitem2 text</fileitem>
    </category>
 
    <category title="Item 2">item 2 text
        <subitem title="subitem21">subitem21 text</fileitem>
        <subitem title="subitem22">subitem22 text</fileitem>
    </category>
</tree>
<tree>
    <category title="Item 1">item 1 text
        <subitem title="subitem1">subitem1 text</fileitem>
        <subitem title="subitem2">subitem2 text</fileitem>
    </category>
    
    <category title="Item 2">item 2 text
        <subitem title="subitem21">subitem21 text</fileitem>
        <subitem title="subitem22">subitem22 text</fileitem>
    </category>
</tree>

I use ElementTree to parse this file and this works okay, however, I now need to remove an item based on its title.

I can loop through the data, but for the life of me I cant work out how to remove the item once I have matched it:

python Syntax (Toggle Plain Text)
    import xml.etree.cElementTree as ET
    ...
    ...
    ...
    self.xml = ET.parse(self.fpath)
    ...
    ...
    ...
    titem = "subitem21"
    xml = self.xml.getroot()
    iterator = xml.getiterator("subitem")
    for item in iterator:
        f = item
        text = item.attrib["title"]
        if text == titem:
            xml.remove(f)
    import xml.etree.cElementTree as ET
    ...
    ...
    ...
    self.xml = ET.parse(self.fpath)
    ...
    ...
    ...
    titem = "subitem21"
    xml = self.xml.getroot()
    iterator = xml.getiterator("subitem")
    for item in iterator:
        f = item
        text = item.attrib["title"]
        if text == titem:
            xml.remove(f)

If I use print statements I can see that I am actually finding the right item, but I just cant work out how to remove it, since it would seem that I should use either xml.remove() or item.remove(), and in either case I get an error stating that "x is not in the list", presumably saying that it cant find and delete the item that it just found!

Can anyone point me in the right direction please?

cheers

Max

MaxVK

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May 5th, 2009

Re: Iterating and removing an element from ElementTree

According to documentation:

Quote ...

Unlike the findXYZ methods this method compares elements based on the instance identity, not on tag value or contents.

Which means that likely your iterator is returning the contents and not the instance itself.

jlm699

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May 5th, 2009

Re: Iterating and removing an element from ElementTree

Hmm, okay, I can run with that - Now how do I get a reference to the instance rather than the contents?

MaxVK

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May 5th, 2009

Re: Iterating and removing an element from ElementTree

Hmm, after taking another look at your method, you must be getting the instance and not just the contents since you're able to call the attrib method... Have you tried using remove(item) instead of remove(f) ?

jlm699

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May 5th, 2009

Re: Iterating and removing an element from ElementTree

Yes. I get the same error, which is simply that the item is not in the list. Iv tried getting the element half a dozen ways, and so far that error is the closest that Iv come to removing an item.

If I just try to "print item" it shows that it is an element, but whichever way I treat it, I get the same error. Kind of driving me nuts now!

[edit]
More specifically I get "ValueError: list.remove(x): x not in list" as the error.

regards

Max

Last edited by MaxVK; May 5th, 2009 at 6:03 pm.

MaxVK

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May 7th, 2009

Re: Iterating and removing an element from ElementTree

Okay, the problem has been solved with some help from others. The problem was that the item I wanted to delete was a child item, and I needed to use the parent to perform the remove:

parent.remove(child)

I ended up with some much simple code, that works nicely providing you keep in mind where in the structure the child to be removed actually is - This code works to remove direct Grandchildren of the Root item! (Of course its easy enough to expand it to remove any items, but Ill leave that to you!)

Python Syntax (Toggle Plain Text)
for x in xml:
            for y in x:
                if y.attrib["title"] == titem:
                    x.remove(y)
                    self.xml.write("output.xml")
                    return
for x in xml:
            for y in x:
                if y.attrib["title"] == titem:
                    x.remove(y)
                    self.xml.write("output.xml")
                    return

I hope this helps someone.

regards

Max

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