A quick and dirty python SUDS script that shows how to get the current session ID using the vSphere API

vsphere_current_session.py

#!/usr/bin/python

import argparse
import suds

parser = argparse.ArgumentParser()
parser.add_argument('-s', '--host', required=True, action='store', help='Remote host to connect to')
parser.add_argument('-u', '--user', required=True, action='store', help='User name to use when connecting to host')
parser.add_argument('-p', '--password', required=True, action='store', help='Password to use when connecting to host')
args = parser.parse_args()

url = "https://%s/sdk/vimService.wsdl" % args.host

client = suds.client.Client(url,location=url)
si = suds.sudsobject.Property("ServiceInstance")
si._type = "ServiceInstance"
sc = client.service.RetrieveServiceContent(si)

client.service.Login(sc.sessionManager, userName=args.user, password=args.password)

property_filter_spec = client.factory.create('ns0:PropertyFilterSpec')
property_spec = client.factory.create('ns0:PropertySpec')
property_spec.pathSet = ['currentSession']
#property_spec.all = True
property_spec.type = "SessionManager"
property_filter_spec.propSet = [property_spec]
object_spec = client.factory.create('ns0:ObjectSpec')
object_spec.obj = sc.sessionManager
object_spec.skip = False
property_filter_spec.objectSet = [object_spec]
options = client.factory.create('ns0:RetrieveOptions')
options.maxObjects = 1
results = client.service.RetrievePropertiesEx(sc.propertyCollector, specSet=[property_filter_spec], options=options)

def get_property(self, name):
    for obj in self.objects:
        for prop in obj.propSet:
            if prop.name == name:
                return prop.val

results.__class__.get_property = get_property

current_session = results.get_property('currentSession')

if current_session:
    print "current session id: %s" % current_session.key
else:
    print "not logged in"