code: def parseExtn(extn=None):
      
  
      if not extn:
          return ('', 0)
  
      try:
          lext = extn.split(',')
      except:
          return ('', 1)
  
      if len(lext) == 1 and lext[0].isdigit():
          return ("", int(lext[0]))
      elif len(lext) == 2:
          return (lext[0], int(lext[1]))
      else:
          return (lext[0], 1)
docs: Parse a string representing a qualified fits extension name as in the
      output of `parseFilename` and return a tuple ``(str(extname),
      int(extver))``, which can be passed to `astropy.io.fits` functions using
      the 'ext' kw.
  
      Default return is the first extension in a fits file.
  
      Examples
      --------
  
      ::
  
          >>> parseExtn('sci, 2')
          ('sci', 2)
          >>> parseExtn('2')
          ('', 2)
          >>> parseExtn('sci')
          ('sci', 1)