http.py 文件源码

def setETag(self, etag):
        """Set an X{entity tag} for the outgoing response.

        That's \"entity tag\" as in the HTTP/1.1 X{ETag} header, \"used
        for comparing two or more entities from the same requested
        resource.\"

        If I am a conditional request, I may modify my response code
        to L{NOT_MODIFIED} or L{PRECONDITION_FAILED}, if appropriate
        for the tag given.

        @param etag: The entity tag for the resource being returned.
        @type etag: string
        @return: If I am a X{If-None-Match} conditional request and
            the tag matches one in the request, I return
            L{http.CACHED<CACHED>} to indicate that you should write
            no body.  Otherwise, I return a false value.
        """
        if etag:
            self.etag = etag

        tags = self.getHeader("if-none-match")
        if tags:
            tags = tags.split()
            if (etag in tags) or ('*' in tags):
                self.setResponseCode(((self.method in ("HEAD", "GET"))
                                      and NOT_MODIFIED)
                                     or PRECONDITION_FAILED)
                return CACHED
        return None