def register_linker(name, linker):
 if (name in predefined_linkers):
  raise ValueError(('Linker name already taken: %s' % name))
 predefined_linkers[name] = linker

def register_linker ( name , linker ) : if ( name in predefined_linkers ) : raise ValueError ( ( 'Linker name already taken: %s' % name ) ) predefined_linkers [ name ] = linker
add a linker which can be referred to by name in mode .