"The issue is that the double() function from MATLAB does not convert the tuple into a double array"
No, the issue is actually that your TUPLE contains non-scalar arrays (which are LISTs i.e. container arrays, not numeric). So rather than calling DOUBLE it would make a lot more sense to call CELL. In fact, that is exactly what MATLAB advises, when you read the message it shows (you can also read this message in your question):
T = pyrun("x = ([1,2],[98,99])","x")
DOUBLE requires that every TUPLE element is a numeric (probably scalar, but I did not check this), which your data are not (ultimately they are LISTs, not numeric):
try
double(T)
catch ME
ME.message
end
Solution One
Lets try CELL instead (which in general makes much more sense for a container array like TUPLE anyway):
C = cell(T)
Converting the nested LISTs is then very easy:
C = cellfun(@double,C,'uni',0)
This is also explained in the MATLAB documentation:
https://www.mathworks.com/help/matlab/matlab_external/handle-data-returned-from-python-function.html
Or more generally:
Solution Two
Another approach is to simply use the correct indexing for accessing the content of a container array (i.e. curly braces), much like what you attempted in your question (except you used parentheses, which just like every other indexing operation using parentheses returns the array itself, not its content):
V1 = double(T{1})
V2 = double(T{2})
Indexing into Python container types is explained in the MATLAB documentation:
Or more generally:
