Recalculate XML child element - python-3.x

Question

Using python3 I am trying to read an xml file and recalculate values based on the attributes within the Item, then write a copy of entire xml file with new values.
Example of xml file (about 10k rows in full file):
<?xml version="1.0" encoding="utf-8"?>
<Items>
<Item id="headscarf_d"
name="{=wW3iouiU}Hijab"
mesh="headscarf_d"
culture="Culture.aserai"
weight="0.5"
value="63"
appearance="1"
Type="HeadArmor">
<ItemComponent>
<Armor head_armor="3"
has_gender_variations="false"
beard_cover_type="type3"
hair_cover_type="all"
modifier_group="cloth_unarmoured"
material_type="Cloth"/>
</ItemComponent>
<Flags Civilian="true"
UseTeamColor="true" />
</Item>
<Item id="open_head_scarf"
name="{=qsVRoGUv}Open Head Scarf"
mesh="aserai_helmet_c"
culture="Culture.aserai"
weight="0.6"
value="174"
appearance="1"
Type="HeadArmor">
<ItemComponent>
<Armor head_armor="5"
has_gender_variations="false"
beard_cover_type="type3"
hair_cover_type="all"
modifier_group="cloth_unarmoured"
material_type="Cloth"/>
</ItemComponent>
<Flags Civilian="true"
UseTeamColor="true" />
</Item>
<Item id="woven_turban"
name="{=ArPvuBYK}Woven Turban"
subtype="head_armor"
mesh="aserai_helmet_h"
culture="Culture.aserai"
weight="0.8"
difficulty="0"
value="250"
appearance="1"
Type="HeadArmor">
<ItemComponent>
<Armor head_armor="6"
has_gender_variations="false"
beard_cover_type="type2"
hair_cover_type="all"
modifier_group="cloth_unarmoured"
material_type="Cloth"/>
</ItemComponent>
<Flags Civilian="true"
UseTeamColor="true" />
</Item>
</Items>
Taking a single item from the example xml,
<Item id="headscarf_d"
name="{=wW3iouiU}Hijab"
mesh="headscarf_d"
culture="Culture.aserai"
weight="0.5"
value="63"
appearance="1"
Type="HeadArmor">
<ItemComponent>
<Armor head_armor="3"
has_gender_variations="false"
beard_cover_type="type3"
hair_cover_type="all"
modifier_group="cloth_unarmoured"
material_type="Cloth"/>
</ItemComponent>
<Flags Civilian="true"
UseTeamColor="true" />
For simplicity say I wanted to take the Item value (63 above example) and divide by 2 (63/2=31.5). Then if the Item's ItemComponent material_type="Cloth" divide by 2 again (31.5/2=15.75). Finally round to an integer before updating the value and repeating for each item then writing the new updated xml file.
I attempted to use Reading, modifying and writing xml but could not get anything useful.

Answer 1

You are probably looking for something along these lines:
from lxml import etree
import math
inv="""[your xml above]"""
doc = etree.XML(inv)
values = doc.xpath('//Item')
materials = doc.xpath('Item//ItemComponent//Armor')
for t, m in zip(values,materials):
if m.attrib['material_type'] == 'Cloth':
val = float(t.attrib['value'])/4
t.attrib['value'] = str(math.ceil(val))
else:
t.attrib['value']= str(math.ceil(val*2))
print(etree.tostring(doc).decode())
The output is your xml with the Items/Item/#value attribute value divided by 2 or 4, as necessary, and rounded up by math.ceil(). Since all Items in your example have cloth as the value of the attribute material_type, they were all divided by 4 and rounded up to:
16
44
63