[python] How to detect a remote webpage is accessible? (in HTTP)

[甜瓜]

Howdy, all,
     I want to use python to detect the accessibility of website.
Currently, I use urllib
to obtain the remote webpage, and see whether it fails. But the problem is that
the webpage may be very large; it takes too long time. Certainly, it
is no need to download
the entire page. Could you give me a good and fast solution?
    Thank you.
--
ShenLei