code: def parse_url(arg, extract, key=None):
      
      return ops.ParseURL(arg, extract, key).to_expr()
docs: Returns the portion of a URL corresponding to a part specified
      by 'extract'
      Can optionally specify a key to retrieve an associated value
      if extract parameter is 'QUERY'
  
      Parameters
      ----------
      extract : one of {'PROTOCOL', 'HOST', 'PATH', 'REF',
                  'AUTHORITY', 'FILE', 'USERINFO', 'QUERY'}
      key : string (optional)
  
      Examples
      --------
      >>> url = "https://www.youtube.com/watch?v=kEuEcWfewf8&t=10"
      >>> parse_url(url, 'QUERY', 'v')  # doctest: +SKIP
      'kEuEcWfewf8'
  
      Returns
      -------
      extracted : string