import codecs, os

filename = "test.utf-16"
if os.path.exists(filename): os.unlink(filename)  # reset

def myOpen():
  return codecs.open(filename, "a", 'UTF-16')
def readThemBack():
  return list( codecs.open(filename, "r", 'UTF-16') )
def clumsyPatch(raw): # you can read it after your first run of this program
  for line in raw:
    if line[0] in (u'\ufffe', u'\ufeff'): # get rid of the BOMs
      yield line[1:]
    else:
      yield line

fout = myOpen()
fout.write(u"ab\n") # to simplify the problem, I only use ASCII chars here
fout.write(u"cd\n")
fout.close()
print readThemBack()
assert readThemBack() == [ u'ab\n', u'cd\n' ]
assert os.stat(filename).st_size == 14  # Only one BOM in the file

fout = myOpen()
fout.write(u"ef\n")
fout.write(u"gh\n")
fout.close()
print readThemBack()
#print list( clumsyPatch( readThemBack() ) )  # later you can enable this fix
assert readThemBack() == [ u'ab\n', u'cd\n', u'ef\n', u'gh\n' ] # fails here
assert os.stat(filename).st_size == 26  # not to mention here: multi BOM appears