docs: def is_sipdir(directory):
      """ Simple check if the supplied directory is a SIP directory.
  
      Parameters
      ----------
      directory: string
          Check if the supplied path is a valid SIP directory
  
  
      Returns
      -------
      is_sipdir: bool
          True if the supplied directory is a SIP directory
      """
      is_sipdir = True
  
      if(not os.path.isfile(directory + os.sep + 'frequencies.dat')):
          is_sipdir = False
  
      if(not os.path.isdir(directory + os.sep + 'invmod')):
          is_sipdir = False
  
      return is_sipdir