code: def __select_builder(lxml_builder, libxml2_builder, cmdline_builder):
      
      if prefer_xsltproc:
          return cmdline_builder
      
      if not has_libxml2:
          # At the moment we prefer libxml2 over lxml, the latter can lead
          # to conflicts when installed together with libxml2.
          if has_lxml:
              return lxml_builder
          else:
              return cmdline_builder
  
      return libxml2_builder
docs: Selects a builder, based on which Python modules are present.