Calling python modules gives error

I have a custom python module and am trying to call a function from it in matlab (2014b). It takes a scalar (integer but there are no checks in the module) as input. Using the documentation from http://www.mathworks.com/help/matlab/matlab_external/call-python-from-matlab.html

hasn't helped. I have created the mymod.py there and can execute all of the commands from that demo. My module Bidiff.py is in the same folder as mymod.py (which has always been my pwd in the session). However, if I try something like

A=py.Bidiff.GenerateNoise(30)

in matlab, I get the error

Undefined variable "py" or function "py.BiDiff.GenerateNoise".

this takes quite a while (2-3 minutes) before it returns the error. The code runs in python; I can import BiDiff into a python session and run

Bidiff.GenerateNoise(30)

and receive the output in under 3 seconds. So the python module is working.

pyversion returns my current installation (2.7) and shows isloaded: 1 (I assume since I ran the demo). If it matters, I am on a Linux machine for this (trying to explain why http://www.mathworks.com/help/matlab/matlab_external/undefined-variable-py-or-function-py-command.html hasn't helped).

Answer 1

[Robert Snoeberger]

Hi Richard,

For the information you have given, there are two possible issues 1) module BiDiff is not imported or 2) function GenerateNoise is not available. Can you access any other functions in your custom python module BiDiff.py?

Answer 2

[Richard]

Hi Robert,

I tried running the other function in the module that I CAN run. It also runs fine in a python prompt after importing the module. However this time, the error from matlab was (I have to pass some python tuples a and b which are generated fine by py.tuple):

A=py.BiDiff.Interfacer(a,b,N)

Undefined variable "py" or class "py.BiDiff.Interfacer"

I would note that Interfacer is a function just like the GenerateNoise, not a class.

Answer 3

[Robert Snoeberger]

Richard, please try the following and let me know if there are any errors:

BiDiff = py.eval('__import__(''BiDiff'')', struct);
func = BiDiff.GenerateNoise;
A = feval(func, int32(30))

When you are working in the python prompt, what is the line you use to import your module?

[Richard]

In python, I type

import BiDiff

and I can then access all functions in that module in the standard way. I ran the first line and get the error

Python Error: No module named BiDiff

[Richard]

I made a mistake in that, I forgot to rerun the

insert(py.sys.path,int32(0),'');

before doing

Bidiff = py.eval('__import__(''BiDiff'')', struct);

However, now I get the following error:

Python Error: /usr/lib/libQVTK.so.5.8: undefined symbol: _ZN12QApplication10commitDataER15QSessionManager

[Robert Snoeberger]

Do you know which import in your custom module is causing this error? I would guess that it is vtk.

[Kevin O'Connor]

I am having the same problem that Richard was having. I did what you asked him to do and when I do that I get a barrage of errors that I do not understand. They are as follows:

>> connectM = py.eval('__import__(''connectM'')', struct);
func = connectM.connectM;
A = feval(func, int32(30))
Error using enginesession>__init__ (line 8)
Python Error: EngineError: MATLAB process session cannot be initialized.

Error in __init__><module> (line 80)
_session = EngineSession()

Error in connectM><module> (line 19)
import matlab.engine

Error in <string>><module> (line 1)

And so I do not understand what is going on. My pyversion all seems valid, and when I use

from connectM import connectM
eng = connectM()

in the python interpreter everything is fine. Nowhere else seems to have any more information on this particular set of errors.

[Robert Snoeberger]

Kevin,

Richard's problem was due to an incompatible version of libQVTK.so being used when calling Python from MATLAB. Your problem is different. Based on the error message "EngineError: MATLAB process session cannot be initialized," you are trying to use matlab.engine within MATLAB. You should post a new question.