This is a python script that can control a local WeMo switch as long as you know the local IP of the WeMo. The script is a fork of pdumoulin's blinky: https://github.com/pdumoulin/blinky.

WeMo.py

#!/usr/bin/python

import re
import urllib2

# Configuration:
# Enter the local IP address of your WeMo in the parentheses of the ip variable below. 
# You may have to check your router to see what local IP is assigned to the WeMo.
# It is recommended that you assign a static local IP to the WeMo to ensure the WeMo is always at that address.
# Uncomment one of the triggers at the end of this script.

ip = ''


class wemo:
	OFF_STATE = '0'
	ON_STATES = ['1', '8']
	ip = None
	ports = [49153, 49152, 49154, 49151, 49155]

	def __init__(self, switch_ip):
		self.ip = switch_ip      
   
	def toggle(self):
		status = self.status()
		if status in self.ON_STATES:
			result = self.off()
			result = 'WeMo is now off.'
		elif status == self.OFF_STATE:
			result = self.on()
			result = 'WeMo is now on.'
		else:
			raise Exception("UnexpectedStatusResponse")
		return result    

	def on(self):
		return self._send('Set', 'BinaryState', 1)

	def off(self):
		return self._send('Set', 'BinaryState', 0)

	def status(self):
		return self._send('Get', 'BinaryState')

	def name(self):
		return self._send('Get', 'FriendlyName')

	def signal(self):
		return self._send('Get', 'SignalStrength')
  
	def _get_header_xml(self, method, obj):
		method = method + obj
		return '"urn:Belkin:service:basicevent:1#%s"' % method
   
	def _get_body_xml(self, method, obj, value=0):
		method = method + obj
		return '<u:%s xmlns:u="urn:Belkin:service:basicevent:1"><%s>%s</%s></u:%s>' % (method, obj, value, obj, method)
	
	def _send(self, method, obj, value=None):
		body_xml = self._get_body_xml(method, obj, value)
		header_xml = self._get_header_xml(method, obj)
		for port in self.ports:
			result = self._try_send(self.ip, port, body_xml, header_xml, obj) 
			if result is not None:
				self.ports = [port]
			return result
		raise Exception("TimeoutOnAllPorts")

	def _try_send(self, ip, port, body, header, data):
		try:
			request = urllib2.Request('http://%s:%s/upnp/control/basicevent1' % (ip, port))
			request.add_header('Content-type', 'text/xml; charset="utf-8"')
			request.add_header('SOAPACTION', header)
			request_body = '<?xml version="1.0" encoding="utf-8"?>'
			request_body += '<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">'
			request_body += '<s:Body>%s</s:Body></s:Envelope>' % body
			request.add_data(request_body)
			result = urllib2.urlopen(request, timeout=3)
			return self._extract(result.read(), data)
		except Exception as e:
			print str(e)
			return None

	def _extract(self, response, name):
		exp = '<%s>(.*?)<\/%s>' % (name, name)
		g = re.search(exp, response)
		if g:
			return g.group(1)
		return response

def output(message):
	print message

switch = wemo(ip)

# Configuration:
# Uncomment only one of the lines below to make the script work.

#output(switch.on())
#output(switch.off())
#output(switch.toggle())
#output(switch.status())

Hi,
Is there a way to retrieve the instant power?
Thanks.