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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 create_sas_token(key_name, shared_access_key, scope, expiry=timedelta(hours=1)):
 """Create a SAS token. :param key_name: The username/key name/policy name for the token. :type key_name: bytes :param shared_access_key: The shared access key to generate the token from. :type shared_access_key: bytes :param scope: The token permissions scope. :type scope: bytes :param expiry: The lifetime of the generated token. Default is 1 hour. :type expiry: ~datetime.timedelta :rtype: bytes """

    shared_access_key = base64.b64encode(shared_access_key)
    abs_expiry = int(time.time()) + expiry.seconds
    return c_uamqp.create_sas_token(shared_access_key, scope, key_name, abs_expiry)