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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 delete_access_key(self, access_key_id, user_name=None):
 """ Delete an access key associated with a user. If the user_name is not specified, it is determined implicitly based on the AWS Access Key ID used to sign the request. :type access_key_id: string :param access_key_id: The ID of the access key to be deleted. :type user_name: string :param user_name: The username of the user """

        params = {'AccessKeyId' : access_key_id}
        if user_name:
            params['UserName'] = user_name
        return self.get_response('DeleteAccessKey', params)