def encode(self):
        # Create the XML document
        doc = Document()
        signed_cred = doc.createElement("signed-credential")

# Declare namespaces
# Note that credential/policy.xsd are really the PG schemas
# in a PL namespace.
# Note that delegation of credentials between the 2 only really works
# cause those schemas are identical.
# Also note these PG schemas talk about PG tickets and CM policies.
        signed_cred.setAttribute("xmlns:xsi", "http://www.w3.org/2001/XMLSchema-instance")
        signed_cred.setAttribute("xsi:noNamespaceSchemaLocation", "http://www.planet-lab.org/resources/foam.sfa.credential.xsd")
        signed_cred.setAttribute("xsi:schemaLocation", "http://www.planet-lab.org/resources/foam.sfa.ext/policy/1 http://www.planet-lab.org/resources/foam.sfa.ext/policy/1/policy.xsd")

# PG says for those last 2:
#        signed_cred.setAttribute("xsi:noNamespaceSchemaLocation", "http://www.protogeni.net/resources/credential/credential.xsd")
#        signed_cred.setAttribute("xsi:schemaLocation", "http://www.protogeni.net/resources/credential/ext/policy/1 http://www.protogeni.net/resources/credential/ext/policy/1/policy.xsd")

        doc.appendChild(signed_cred)  
        
        # Fill in the <credential> bit        
        cred = doc.createElement("credential")
        cred.setAttribute("xml:id", self.get_refid())
        signed_cred.appendChild(cred)
        append_sub(doc, cred, "type", "privilege")
        append_sub(doc, cred, "serial", "8")
        append_sub(doc, cred, "owner_gid", self.gidCaller.save_to_string())
        append_sub(doc, cred, "owner_urn", self.gidCaller.get_urn())
        append_sub(doc, cred, "target_gid", self.gidObject.save_to_string())
        append_sub(doc, cred, "target_urn", self.gidObject.get_urn())
        append_sub(doc, cred, "uuid", "")
        if not self.expiration:
            self.set_expiration(datetime.datetime.utcnow() + datetime.timedelta(seconds=DEFAULT_CREDENTIAL_LIFETIME))
        self.expiration = self.expiration.replace(microsecond=0)
        append_sub(doc, cred, "expires", self.expiration.isoformat())
        privileges = doc.createElement("privileges")
        cred.appendChild(privileges)

        if self.privileges:
            rights = self.get_privileges()
            for right in rights.rights:
                priv = doc.createElement("privilege")
                append_sub(doc, priv, "name", right.kind)
                append_sub(doc, priv, "can_delegate", str(right.delegate).lower())
                privileges.appendChild(priv)

        # Add the parent credential if it exists
        if self.parent:
            sdoc = parseString(self.parent.get_xml())
            # If the root node is a signed-credential (it should be), then
            # get all its attributes and attach those to our signed_cred
            # node.
            # Specifically, PG and PLadd attributes for namespaces (which is reasonable),
            # and we need to include those again here or else their signature
            # no longer matches on the credential.
            # We expect three of these, but here we copy them all:
#        signed_cred.setAttribute("xmlns:xsi", "http://www.w3.org/2001/XMLSchema-instance")
# and from PG (PL is equivalent, as shown above):
#        signed_cred.setAttribute("xsi:noNamespaceSchemaLocation", "http://www.protogeni.net/resources/credential/credential.xsd")
#        signed_cred.setAttribute("xsi:schemaLocation", "http://www.protogeni.net/resources/credential/ext/policy/1 http://www.protogeni.net/resources/credential/ext/policy/1/policy.xsd")

            # HOWEVER!
            # PL now also declares these, with different URLs, so
            # the code notices those attributes already existed with
            # different values, and complains.
            # This happens regularly on delegation now that PG and
            # PL both declare the namespace with different URLs.
            # If the content ever differs this is a problem,
            # but for now it works - different URLs (values in the attributes)
            # but the same actual schema, so using the PG schema
            # on delegated-to-PL credentials works fine.

            # Note: you could also not copy attributes
            # which already exist. It appears that both PG and PL
            # will actually validate a slicecred with a parent
            # signed using PG namespaces and a child signed with PL
            # namespaces over the whole thing. But I don't know
            # if that is a bug in xmlsec1, an accident since
            # the contents of the schemas are the same,
            # or something else, but it seems odd. And this works.
            parentRoot = sdoc.documentElement
            if parentRoot.tagName == "signed-credential" and parentRoot.hasAttributes():
                for attrIx in range(0, parentRoot.attributes.length):
                    attr = parentRoot.attributes.item(attrIx)
                    # returns the old attribute of same name that was
                    # on the credential
                    # Below throws InUse exception if we forgot to clone the attribute first
                    oldAttr = signed_cred.setAttributeNode(attr.cloneNode(True))
                    if oldAttr and oldAttr.value != attr.value:
                        msg = "Delegating cred from owner %s to %s over %s replaced attribute %s value '%s' with '%s'" % (self.parent.gidCaller.get_urn(), self.gidCaller.get_urn(), self.gidObject.get_urn(), oldAttr.name, oldAttr.value, attr.value)
                        #raise CredentialNotVerifiable("Can't encode new valid delegated credential: %s" % msg)

            p_cred = doc.importNode(sdoc.getElementsByTagName("credential")[0], True)
            p = doc.createElement("parent")
            p.appendChild(p_cred)
            cred.appendChild(p)
        # done handling parent credential

        # Create the <signatures> tag
        signatures = doc.createElement("signatures")
        signed_cred.appendChild(signatures)

        # Add any parent signatures
        if self.parent:
            for cur_cred in self.get_credential_list()[1:]:
                sdoc = parseString(cur_cred.get_signature().get_xml())
                ele = doc.importNode(sdoc.getElementsByTagName("Signature")[0], True)
                signatures.appendChild(ele)
                
        # Get the finished product
        self.xml = doc.toxml()
dataset/ETHPy150Open fp7-ofelia/ocf/ofam/src/src/foam/sfa/trust/credential.py/Credential.encode/original