Using MATLAB Engine API for Python

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Ankita Tondwalkar 2022-3-27

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1682024-using-matlab-engine-api-for-python

评论： Ankita Tondwalkar 2022-9-26

I have a variable A= 25 (1X1 double) in my MATLAB workspace and I am using the MATLAB Engine API to call it in python by using the following code.

import matlab.engine

eng = matlab.engine.start_matlab()

var = eng.workspace['A']

print(var)

I am getting the following error message:

Error using matlab.internal.engine.getVariable

Undefined variable 'A'.

Traceback (most recent call last):

File "readingdata.py", line 20, in <module>

test = eng.workspace['A']

File "/usr/local/lib/python3.8/dist-packages/matlab/engine/matlabengine.py", line 120, in __getitem__

future = _method(attr)

File "/usr/local/lib/python3.8/dist-packages/matlab/engine/matlabengine.py", line 70, in __call__

return FutureResult(self._engine(), future, nargs, _stdout,

File "/usr/local/lib/python3.8/dist-packages/matlab/engine/futureresult.py", line 67, in result

return self.__future.result(timeout)

File "/usr/local/lib/python3.8/dist-packages/matlab/engine/fevalfuture.py", line 82, in result

self._result = pythonengine.getFEvalResult(self._future,self._nargout, None, out=self._out, err=self._err)

matlab.engine.MatlabExecutionError:

File /usr/local/MATLAB/R2022a/toolbox/matlab/external/engines/engine_api/+matlab/+internal/+engine/getVariable.m, line 27, in getVariable

Undefined variable 'A'.

I could do the same using scipy.io

Is there something I am missing?

回答（1 个）

Kojiro Saito 2022-3-28

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1682024-using-matlab-engine-api-for-python#answer_928354

在 MATLAB Online 中打开

It's because engine.start_matlab launches a new MATALB session and there's no variable in workspace.

You need to create a session to a running MATLAB as described in this document.

In MATLAB, you need to call matlab.engine.shareEngine.

[MATLAB side]

A = 25;
matlab.engine.shareEngine

Then, you need to create a session from Python using engine.connect_matlab not engine.start_matlab.

[Python side]

import matlab.engine
eng = matlab.engine.connect_matlab()
var = eng.workspace['A']
print(var)

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Ankita Tondwalkar 2022-5-4

This problem resulted from that fact how indexing works differenty in MATLAB and Python. I made sure while callig in Python I followed the indexing rule for Python.

Ankita Tondwalkar 2022-9-26

Hello,

I am trying to access predefined enviromen ("BasicGridWorld") variable, obsInfo and actInfo present in MATLAB workspace in Python.

While doing so, I am able to find my MATLAB session but unable to connect to it.

In my Python terminal I am getting the following error:

matlab.engine.EngineError: Unable to connect to MATLAB session 'MATLAB_3052'.

In MATLAB I am using the share engine command (but I get the error that "The current MATLAB session is shared already")while in Python I have the matlab.engine.connect_matlab(). Can anyone let me know if I am missing something?

Thanks,

Ankita

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