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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def useNonce(self, server_url, timestamp, salt):
 """Return whether this nonce is valid. str -> bool """

        if abs(timestamp - time.time()) > nonce.SKEW:
            return False

        if server_url:
            proto, rest = server_url.split('://', 1)
        else:
            # Create empty proto / rest values for empty server_url,
            # which is part of a consumer-generated nonce.
            proto, rest = '', ''

        domain = _filenameEscape(rest.split('/', 1)[0])
        url_hash = _safe64(server_url)
        salt_hash = _safe64(salt)

        filename = '%08x-%s-%s-%s-%s' % (timestamp, proto, domain,
                                         url_hash, salt_hash)

        filename = os.path.join(self.nonce_dir, filename)
        try:
            fd = os.open(filename, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0200)
        except OSError, why:
            if why.errno == EEXIST:
                return False
            else:
                raise
        else:
            os.close(fd)
            return True