Storing output of python call to class

I'm trying to make a class that will wrap Python's sigmf module. My first step is to load the sigmf file using a python call and store it for later, but I'm not sure how to store it.

My current class is

classdef SigMF

% Wrapper class for python sigmf module

properties

sigmf

end

methods

function obj = fromfile(obj, filename)

% Create a python sigmffile and store for processing

obj.sigmf = py.sigmf.sigmffile.fromfile(filename);

end

function samples = read_samples(obj, start_idx, count)

% Read a number of samples from a given start index

samples = obj.sigmf.read_samples(pyargs("start_index", int64(start_idx-1), "count", int64(count)));

end

end

end

I'm calling it using

x = SigMF()

x.fromfile("test")

This doesn't fail, but it doesn't store the output, so the call to read_samples doesn't work. I can run it step by step in the command line or a script as

x = py.sigmf.sigmffile.fromfile("test")

x.read_samples(pyargs("start_index", int32(0), "count", int32(100)))

I could make read_samples load the file and read samples, loading the file can be slow for large file sizes, so I'd like to just load it once and access it anytime I need it.

Answer 1

[Neha]

Hi Trey,

I understand that you want to create a class that will wrap the "sigmf" module from Python. By default, MATLAB classes are value classes. Therefore, any modifications made to a property in a method do not persist unless the function actually returns the modified object as an output argument.

To resolve this, you can reassign the object with the output of the "fromfile" function:

x=x.fromfile("test");
samples=x.read_samples(1, 100);

Another way to avoid this issue would be to inherit the "handle" class:

classdef SigMF < handle
    ...
end

For more information about the difference between value and handle classes, you can refer to the following documentation link:

https://in.mathworks.com/help/matlab/matlab_oop/comparing-handle-and-value-classes.html

Hope this helps!