qgis.utils.iface.mapCanvas().refresh()

layers = qgis.utils.iface.legendInterface().layers()
  for layer in layers:
      layer.triggerRepaint()

def md5checksum(fp):
        import hash
    with open(fp, 'rb') as fh:
        m = hashlib.md5()
        while True:
            data = fh.read(8192)
            if not data:
                break
            m.update(data)
        return m.hexdigest()

import time
import copy

a,b = str(),str()
while True:
    a =  md5checksum(fp) # file
    if a != b:  # the file has changed, do what you want
        myLayer.triggerRepaint()
        b = copy.copy(a) #shallow copy, otherwise a and b will point at the same object
    else:
        sleep.time(1) #wait for 1 sec, then recheck