code: def init_passbands(refresh=False):
      
      global _initialized
  
      if not _initialized or refresh:
          # load information from online passbands first so that any that are
          # available locally will override
          online_passbands = list_online_passbands(full_dict=True, refresh=refresh)
          for pb, info in online_passbands.items():
              _pbtable[pb] = {'fname': None, 'atms': info['atms'], 'pb': None}
  
          # load global passbands (in install directory) next and then local
          # (in .phoebe directory) second so that local passbands override
          # global passbands whenever there is a name conflict
          for path in [_pbdir_global, _pbdir_local]:
              for f in os.listdir(path):
                  if f=='README':
                      continue
                  init_passband(path+f)
  
          #Check if _pbdir_env has been set and load those passbands too
          if not _pbdir_env == None:
              for path in [_pbdir_env]:
                  for f in os.listdir(path):
                      if f=='README':
                          continue
                      init_passband(path+f)
  
  
          _initialized = True
docs: This function should be called only once, at import time. It
      traverses the passbands directory and builds a lookup table of
      passband names qualified as 'pbset:pbname' and corresponding files
      and atmosphere content within.