from xml.etree import ElementTree as ET

tree = ET.parse('package.opf')
root = tree.getroot()
ns = {'opf':  'http://www.idpf.org/2007/opf'}
manifest = root.find('opf:manifest', ns)
base_url = ""

for item in manifest.findall('opf:item', ns):
    print(base_url+item.attrib['href'])