how to keep the xml-stylesheet?

I want to keep the xml-stylesheet. But it doesn't work. i use python to modify the xml for deploy hadoop automaticly

XML:

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

<!-- Put site-specific property overrides in this file. -->

<configuration>
    <property>
　　　　<name>fs.default.name</name>
　　　　<value>http://hdfsc11:9000</value>
　　</property>
</configuration>

Code:

from xml.etree.ElementTree import ElementTree as ET

def modify_core_site(namenode_hostname):
    tree = ET()
    tree.parse("pkg/core-site.xml")
    root = tree.getroot()
    for p in root.iter("property"):
        name = p.find("name").text
        if name == "fs.default.name":
            text = "hdfs://%s:9000" % namenode_hostname
            p.find("value").text = text
    tree.write("pkg/tmp.xml", encoding="utf-8", xml_declaration=True)

modify_core_site("c80")

Result:

<?xml version='1.0' encoding='utf-8'?>
<configuration>
    <property>
　　　　<name>fs.default.name</name>
　　　　<value>http://hdfsc80:9000</value>
　　</property>
</configuration>

The xml-stylesheet disappear... How can i keep this?