Encapsulates an argument in a tuple, if it's not already iterable.

def AsIter(arg):
  """Encapsulates an argument in a tuple, if it's not already iterable."""
  if isinstance(arg, string_types):
    rslt = [arg]
  elif isinstance(arg, collections.Iterable):
    rslt = arg
  elif not arg:
    rslt = []
  else:
    rslt = [arg]
  return tuple(rslt)