Calling matlab.eng​ine.connec​t_matlab() twice freezes Python

I can connect to a named running MATLAB session from Python with:

In [8]: matlab.engine.connect_matlab('MY_SESSION')

But if I call it a second time Python hangs for about a minute before finally saying it can not connect

In [8]: matlab.engine.connect_matlab('MY_SESSION')
Out[8]: <matlab.engine.matlabengine.MatlabEngine at 0x1648f46a370>

In [9]: matlab.engine.connect_matlab('MY_SESSION')

...
    
EngineError: Unable to connect to MATLAB session 'MY_SESSION'.

I can not find a way of testing if MY_SESSION already exists. I also can not find a way to close a connection that already exists in a different scope. Are those things possible?

Answer 1

[Chris]

names = matlab.engine.find_matlab()
if 'MY_SESSION' in names:
    eng = matlab.engine.connect_matlab('MY_SESSION')

You can del(eng) to close the connection in the present scope, but I'm not sure about forcing it closed from somewhere else.

Since Matlab takes a bit to do its thing, connecting/reconnecting will sometimes throw an error. You might use a try/except or a while loop to handle the error in a python script/program.

[Rob Campbell]

I don't think that if statement helps. I am connecting to a MATLAB session that already exists and is named. I am pretty sure that matlab.engine.find_matlab() will return the name of the session regardless of whether or not I have connected to it.

[Chris]

@Rob Campbell If you name the connection (eng here) in the python shell and delete it when you're done, I don't think it should do anything funky in between? And I can connect to the shared session simultaneously from multiple shells. So maybe I'm not understanding the issue.

[Rob Campbell]

If I try to connect to it twice from the same shell it locks the terminal for a minute the second time then issues an arror. I didn't try different shells. Because I have this issue I was looking for a way to tell if a connection is under way.

[Chris]

Then if the variable is present, the connection is there. Make a function that tests that condition before connecting.

[Rob Campbell]

We are getting side tracked now.

I want a way to test whether the connection has been made and it looks like that does not exist.

Thanks for trying, though.