Ok. Found the solution.
The importance is to use this:

Task.add_requirements("requirements.txt")
task = Task.init(project_name='hieutest', task_name='foo',reuse_last_task_id=False)

And not:

task = Task.init(project_name='hieutest', task_name='foo',reuse_last_task_id=False)
task.add_requirements("requirements.txt")