docs: def get_fwhm(expnum, ccd, prefix=None, version='p'):
      """Get the FWHM computed for the given expnum/ccd combo.
  
      @param expnum:
      @param ccd:
      @param prefix:
      @param version:
      @return:
      """
  
      uri = get_uri(expnum, ccd, version, ext='fwhm', prefix=prefix)
      filename = os.path.basename(uri)
  
      try:
          return fwhm[uri]
      except:
          pass
  
      try:
          fwhm[uri] = float(open(filename, 'r').read())
          return fwhm[uri]
      except:
          pass
  
      try:
          fwhm[uri] = float(open_vos_or_local(uri).read())
          return fwhm[uri]
      except Exception as ex:
          logger.error(str(ex))
          fwhm[uri] = 4.0
          return fwhm[uri]