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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 list_task_definitions(self):
 """ Filtering not implemented """

        task_arns = []
        for task_definition_list in self.task_definitions.values():
            task_arns.extend(
                [task_definition.arn for task_definition in task_definition_list])
        return task_arns