I recommended you to use lxml instead of xml.dom.minidom.
Using lxml.html / cssselect:
import lxml.html
root = lxml.html.fromstring(document_string)
for elem in root.cssselect('elem.class'):
print(elem.tag)
print(elem.get('src'))
Using lxml.etree / xpath:
import lxml.etree
root = lxml.etree.fromstring(document_string)
for elem in root.xpath('.//elem[contains(@class, "class")]'):
print(elem.tag)
print(elem.get('src'))