def _error_on_bad_paths(fs, paths):
 for path in paths:
  if (path == '-'):
   return
  if fs.exists(path):
   return
 raise ValueError(('At least one valid path is required. None found in %s' % paths))

def _error_on_bad_paths ( fs , paths ) : for path in paths : if ( path == '-' ) : return if fs . exists ( path ) : return raise ValueError ( ( 'At least one valid path is required. None found in %s' % paths ) )
raise an exception if there is not at least one valid path .