[Python] why always Address 'http://127.0.0.1:8050' already in use?

I am doing plotly dash, and sometimes not matter how many other ports I change to use, it always give me below error. Any reason? I even shutdown jupyter notebook and re-launch it and I still got same error. so I am desperate somehome. Thanks for your help.

OSError: Address 'http://127.0.0.1:8052' already in use. Try passing a different port to run_server.


if __name__ == "__main__":
app.run_server(mode='external',debug=True,port=8052)

---------------------------------------------------------------------------
OSError Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_23784/3219569651.py in <module>
1 if __name__ == "__main__":
2 #app.run_server(mode='inline',debug=True,port=8051)
----> 3 app.run_server(mode='external',debug=True,port=8052)

~\miniconda3\envs\dash_project\lib\site-packages\jupyter_dash\jupyter_app.py in run_server(self, mode, width, height, inline_exceptions, **kwargs)
317 )
318
--> 319 wait_for_app()
320
321 if JupyterDash._in_colab:

~\miniconda3\envs\dash_project\lib\site-packages\retrying.py in wrapped_f(*args, **kw)
47 @six.wraps(f)
48 def wrapped_f(*args, **kw):
---> 49 return Retrying(*dargs, **dkw).call(f, *args, **kw)
50
51 return wrapped_f

~\miniconda3\envs\dash_project\lib\site-packages\retrying.py in call(self, fn, *args, **kwargs)
210 if not self._wrap_exception and attempt.has_exception:
211 # get() on an attempt with an exception should cause it to be raised, but raise just in case
--> 212 raise attempt.get()
213 else:
214 raise RetryError(attempt)

~\miniconda3\envs\dash_project\lib\site-packages\retrying.py in get(self, wrap_exception)
245 raise RetryError(self)
246 else:
--> 247 six.reraise(self.value[0], self.value[1], self.value[2])
248 else:
249 return self.value

~\miniconda3\envs\dash_project\lib\site-packages\six.py in reraise(tp, value, tb)
717 if value.__traceback__ is not tb:
718 raise value.with_traceback(tb)
--> 719 raise value
720 finally:
721 value = None

~\miniconda3\envs\dash_project\lib\site-packages\retrying.py in call(self, fn, *args, **kwargs)
198 while True:
199 try:
--> 200 attempt = Attempt(fn(*args, **kwargs), attempt_number, False)
201 except:
202 tb = sys.exc_info()

~\miniconda3\envs\dash_project\lib\site-packages\jupyter_dash\jupyter_app.py in wait_for_app()
310 host=host, port=port, token=JupyterDash._token
311 )
--> 312 raise OSError(
313 "Address '{url}' already in use.\n"
314 " Try passing a different port to run_server.".format(

OSError: Address 'http://127.0.0.1:8052' already in use.
Try passing a different port to run_server.

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