code: def build_prefixes(namespaces=None):
      
      if namespaces is None:
          namespaces = [
              ('bf', str(BIBFRAME)),
              ('schema', str(SCHEMA_ORG))
          ]
      output = "PREFIX {}: <{}>\n".format(
          namespaces[0][0],
          namespaces[0][1])
      if len(namespaces) == 1:
          return output
      else:
          for namespace in namespaces[1:]:
              output += "PREFIX  {}: <{}>\n".format(namespace[0], namespace[1])
      return output
docs: Internal function takes a list of prefix, namespace uri tuples and
      generates a SPARQL PREFIX string.
  
      Args:
          namespaces(list): List of tuples, defaults to BIBFRAME and
                            Schema.org
  
      Returns:
          string