code: def find_language(script, exts=None):
      
      if not script.isfile():
          return None
      if script.ext:
          return ext_language(script.ext, exts)
      shebang = script.shebang()
      return shebang and str(shebang.name) or None
docs: Determine the script's language  extension
  
      >>> this_script = __file__.rstrip('c')
      >>> find_language(makepath(this_script)) == 'python'
      True
  
      If exts are given they restrict which extensions are allowed
      >>> find_language(makepath(this_script), ('.sh', '.txt')) is None
      True
  
      If there is no extension, but shebang is present, then use that
      (Expecting to find "#!" in ~/.bashrc for this test,
          but ~/.bashrc might not exist - then there's no language)
  
      >>> bashrc = home() / '.bashrc'
      >>> find_language(bashrc) in ('bash', None)
      True