How to load .mat file into workspace using Matlab Engine API for Python?

Question

I have a .mat workspace file containing 4 character variables. These variables contain paths to various folders I need to be able to cd to and from relatively quickly. Usually, when using only Matlab I can load this workspace as follows (provided the .mat file is in the current directory).

load paths.mat

Currently I am experimenting with the Matlab Engine API for Python. The Matlab help docs recommend using the following Python formula to send variables to the current workspace in the desktop app:

import matlab.engine
eng = matlab.engine.start_matlab()
x = 4.0
eng.workspace['y'] = x
a = eng.eval('sqrt(y)')
print(a)

Which works well. However the whole point of the .mat file is that it can quickly load entire sets of variables the user is comfortable with. So the above is not efficient when trying to load the workspace.

I have also tried two different variations in Python:

eng.load("paths.mat")
eng.eval("load paths.mat")

The first variation successfully loads a dict variable in Python containing all four keys and values but this does not propagate to the workspace in Matlab. The second variation throws an error:

File "", line unknown SyntaxError: Error: Unexpected MATLAB expression.

How do I load up a workspace through the engine without having to manually do it in Matlab? This is an important part of my workflow....

Answer 1

You didn't specify the number of output arguments from the MATLAB engine, which is a possible reason for the error.

I would expect the error from eng.load("paths.mat") to read something like

TypeError: unsupported data type returned from MATLAB

The difference in error messages may arise from different versions of MATLAB, engine API...

In any case, try specifying the number of output arguments like so,

eng.load("paths.mat", nargout=0)