使用lxml：
import lxml.etree as le
with open('doc.xml','r') as f:
doc=le.parse(f)
for elem in doc.xpath('//*[attribute::lang]'):
if elem.attrib['lang']=='en':
elem.attrib.pop('lang')
else:
parent=elem.getparent()
parent.remove(elem)
print(le.tostring(doc))
产量
<root>
<elm>Common content</elm>
<elm>
<elm>Content EN</elm>
</elm>
<elm>Common content</elm>
<elm>Content EN</elm>
<elm>
<elm>Content EN</elm>
<elm>Content EN</elm>
</elm>
</root>
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