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在运行CORE tutorial 3中的mobility示例时，出现如下错误：

当看到这个问题的时候，并没有仔细去分析日志和现象，在core-daemon的进程打印界面只看了一下最后的出错堆栈：

2024-06-27 10:43:48,614 - ERROR - _server:_call_behavior - Exception calling application: int() argument must be a string, a bytes-like object or a real number, not ‘NoneType’
Traceback (most recent call last):
File “/opt/core/venv/lib/python3.10/site-packages/grpc/_server.py”, line 494, in _call_behavior
response_or_iterator = behavior(argument, context)
File “/opt/core/venv/lib/python3.10/site-packages/core/api/grpc/server.py”, line 916, in MobilityAction
node.mobility.stop(move_initial=True)
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 1095, in stop
super().stop(move_initial=move_initial)
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 839, in stop
self.session.mobility.sendevent(self)
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 209, in sendevent
end_time = int(model.endtime)
TypeError: int() argument must be a string, a bytes-like object or a real number, not ‘NoneType’

然而，从这里很难看出什么问题。在网上各种搜索关键字也是毫无收获。还怀疑是python3.10的版本问题，准备退回python3.9再试试。最后都是无劳而返。
偶然又留意了一下core-daemon最开始出错的打印，才发现如下日志：

2024-06-27 10:42:13,978 - INFO - mobility:update_config - ns-2 scripted mobility configured for WLAN 3 using file: /usr/share/core/examples/tutorials/tutorial3/movements1.txt
2024-06-27 10:42:13,979 - ERROR - mobility:startup - mobility startup error
Traceback (most recent call last):
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 136, in startup
self.set_model(node, model, config)
File “/opt/core/venv/lib/python3.10/site-packages/core/config.py”, line 360, in set_model
node.setmodel(model_class, config)
File “/opt/core/venv/lib/python3.10/site-packages/core/nodes/network.py”, line 754, in setmodel
self.mobility.update_config(config)
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 904, in update_config
self.readscriptfile()
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 916, in readscriptfile
file_path = self.findfile(self.file)
File “/opt/core/venv/lib/python3.10/site-packages/core/location/mobility.py”, line 998, in findfile
raise CoreError(f"invalid file: {file_path}")
core.errors.CoreError: invalid file: /usr/share/core/examples/tutorials/tutorial3/movements1.txt

原来这一段才是出错的根本原因。而且在日志中的原因也说明非常明白:movements1.txt有问题。我检查了一下，原因是我的系统对应路径不存在这个文件。于是重新修改了一下此文件对应的路径，可以顺利运行此示例程序了。
现在在回头看这个问题出现时的现象，在wlan3 mobility player这个窗口上也显示了movements1.txt的路径信息，只是自己没有留意或者在意，导致问题的根本原因未被及时发现。
总结此次教训，产生的原因是未仔细查看所有的日志，未仔细观察所有的现象和界面信息，太过于浮躁。