How to get values with python from xml file

Question

I need some help. I have this XML:

<?xml version="1.0"?>
<WDAT>
<EMOD>
      <MATERIAL number="1.2345">
            <Values>
                      <X>20.0</X>
                      <Y>200.0</Y>
            </Values>
            <Values>
                      <X>100.0</X>
                      <Y>190.0</Y>
            </Values>
            <Values>
                      <X>200.0</X>
                      <Y>185.0</Y>
            </Values>
            <Values>
                      <X>300.0</X>
                      <Y>180.0</Y>
            </Values>
            <Values>
                      <X>400.0</X>
                      <Y>175.0</Y>
            </Values>
    </MATERIAL>
</EMOD>
</WDAT>

I want to get an array with the X-Y values for the material number 1.2345, for example.

tree_materials = ET.parse(r"materials.xml")
root_materials = tree_materials.getroot()
materials = root_materials.findall('EMOD/MATERIAL')
material = tree_materials.findall(".//MATERIAL[@number='1.2345']")
valuess = material.findall('X')

The variable "material" has the correct memory address, but I have difficulties to get the values from X and Y.

Thanks.

Rafael

Corley Brigman · Accepted Answer · 2013-10-16 13:13:54Z

Underneath 'MATERIAL', you have two levels - so you need to pass both levels to findall. You could do:

material = tree_materials.find(".//MATERIAL[@number='1.2345']")
lx = material.findall('Values/X')
ly = material.findall('Values/Y')
points = zip([x.text for x in lx], [y.text for y in ly])

However, you really have to trust your XML to do that - if someone accidentally gave you a file like this:

        <Values>
                  <X>200.0</X>
                  <Y>185.0</Y>
        </Values>
        <Values>
                  <Y>180.0</Y>
        </Values>
        <Values>
                  <X>400.0</X>
                  <Y>175.0</Y>
        </Values>

then you would end up with (200.0, 185.0), (180.0, 175.0) and since zip stops at the shortest item, the 400.0 would just get silently dropped and you might not even know. Explicit is better:

values = material.findall('Values')
points = [(v.find('X').text, v.find('Y').text) for v in values]

If an X or Y node is not present, this will throw an exception, and you'll see it immediately.

You'll need to do another list comprehension to cast these to float, but you can already do that.

Alexander Zhukov · Accepted Answer · 2013-10-16 12:55:11Z

1

In the last 2 lines you can do the following:

    material = tree_materials.find(".//MATERIAL[@number='1.2345']")
    xs = material.findall('X')
    ys = material.findall('Y')
    values = zip([x.text for x in xs], [x.text for x in xs])

this will output the list of tuples like [("20.0", "200.0")...]

edited Oct 16, 2013 at 12:55

answered Oct 16, 2013 at 11:39

Alexander Zhukov

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3 Comments

user2886173 Over a year ago

Thanks for the quick answer. I checked the memory address of "material ", it is ok. But I get an error in the last line: KeyError: '()'

user2886173 Over a year ago

I get now "AttributeError: 'list' object has no attribute 'text'". I am near to the solution, but I dont understand why dont works. I know, it has to be easy.... i am learning. Thanks.

Alexander Zhukov Over a year ago

Sorry, that was my fault. I was to lazy to check the solution first.

user278064 · Accepted Answer · 2013-10-16 13:38:50Z

0

material = tree_materials.xpath("//MATERIAL[@number='1.2345']")[0]
x_values = [x.text for x in material.xpath("//X")]
y_values = [y.text for y in material.xpath("//Y")]
xy_values = zip(x_values, y_values)

answered Oct 16, 2013 at 13:38

user278064

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