def createURIString(valueString, delimiter, vocab):
  """This function takes a delimiter separted string of values and returns a string
     in which every of these values is prefixed with the specified vocab URI.

  >>> createURIString('nl;fr;de', ';', 'http://id.loc.gov/vocabulary/languages/')
  'http://id.loc.gov/vocabulary/languages/nl;http://id.loc.gov/vocabulary/languages/fr;http://id.loc.gov/vocabulary/languages/de'

  An empty input string results in an empty output string
  >>> createURIString('', ';', 'http://id.loc.gov/vocabulary/languages/')
  ''

  Only a delimiter results in an empty string
  >>> createURIString(';', ';', 'http://id.loc.gov/vocabulary/languages/')
  ''

  """

  uris = []
  urisString = ""
  values = valueString.split(delimiter)
  if len(values) > 1: 
    for v in values:
      if len(v) > 0:
        uris.append(vocab + v) 
    urisString = ';'.join(uris)
  elif len(values) == 1:
    if len(values[0]) > 0:
      urisString = vocab + valueString
  else:
    urisString = ''

  return urisString