Using Matlab in Python

Question

I'm trying to execute matlab functions in python using the Matlab python package. However, when running a simple example from the Mathworks website, I am getting an error message. When I run the code:

import matlab.engine
eng = matlab.engine.start_matlab()
a = matlab.double([1,4,9,16,25])
b = eng.sqrt(a)
print(b)

I get the error message:

 File "/dir/Trying.py", line 27, in <module>
 a = matlab.double([1,4,9,16,25])
 File "//anaconda/envs/netcdf/lib/python2.7/site-packages/matlab/mlarray.py", line 51, in __init__
 raise ex
TypeError: 'NoneType' object is not callable

What does this error mean? I can call functions that don't include lists OK but as soon as I try to pass a vector/list through I get the same error. I need to pass m x n arrays through so this is the key to doing that.

Thanks

• Ville: Your code actually works.... Maybe your python version is not compatible with your Matlab version?

Answer 1

you are calling .double form matlab which is not define, I think you need to import matlab as well, from https://www.mathworks.com/help/compiler_sdk/python/matlab-arrays-as-python-variables.html. P/s: I did not use matlab before

import matlab.engine
import matlab
eng = matlab.engine.start_matlab()
a = matlab.double([1,4,9,16,25])
b = eng.sqrt(a)
print(b)

• RH_data_maths: Thanks for your answer. I thought that would do the trick but I'm still getting the same error message... does it work for you?

Answer 2

According to https://nl.mathworks.com/help/matlab/matlab_external/get-started-with-matlab-engine-for-python.html

The function Double is contained in the package matlab and not matlab.engine. Have you tried just importing the package matlab?

import matlab

• RH_data_maths: Thanks. I've added this in now (stupid to forget..) but it's still giving me the same error message. Has it worked for you?
• kwant: I installed the matlab package and ran your script and it is working with no errors (also without the import matlab line). Perhaps try reinstalling the package?
• RH_data_maths: I restarted spyder, ran the code and it was fine. Then I ran the code again and the error popped up. So I connected to a new kernal and the same thing happened again - it seems to work fine on the first run but then I must connect to a new kernal... weird.