colon operator in compiled python package

Hi, I compiled one python package from a matlab one using library compiler. Everything went well until I did a test in Python’s Interpreter. In my Matlab code, I have a function called returnS_test_compiler with a line

f = (fRange(1):fRange(2):fRange(3))';

which generates a list and then "transpose" it.

I assume by compiling the code into python package, I do not need to modify anything in the code. So when I call this returnS_test_compiler in python imported as a python package, it gives the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/MATLAB/MATLAB_Runtime/v97/toolbox/compiler_sdk/pysdk_py/matlab_pysdk/runtime/deployablefunc.py", line 80, in __call__
    nlhsWasSpecified, stdoutObj, stderrObj).result()
  File "/usr/local/MATLAB/MATLAB_Runtime/v97/toolbox/compiler_sdk/pysdk_py/matlab_pysdk/runtime/futureresult.py", line 135, in result
    raise e
  File "/usr/local/MATLAB/MATLAB_Runtime/v97/toolbox/compiler_sdk/pysdk_py/matlab_pysdk/runtime/futureresult.py", line 123, in result
    raise e
  File "/usr/local/MATLAB/MATLAB_Runtime/v97/toolbox/compiler_sdk/pysdk_py/matlab_pysdk/runtime/futureresult.py", line 113, in result
    self._nlhs, out=self._out, err=self._err)
matlab_pysdk.runtime.MatlabRuntimeError: An error occurred when evaluating the result from a function. Details: 
  File /root/.mcrCache9.7/return0/returnS_test/returnS_test_compiler.m, line 15, in returnS_test_compiler
Undefined function 'colon' for input arguments of type 'cell'.

It seems that it is complaining ( : : ) is not recognisable as a python sentence. Any suggestions?

Answer 1

[Steven Lord]

The variable fRange is a cell array. The colon operator doesn't know how to work on cell arrays.

a = {1};
b = {10};
x = a:b % throws error

Operator ':' is not supported for operands of type 'cell'.

To get this to work, pass the contents of the cells in the cell arrays to the colon operator.

a = {1};
b = {10};
x = a{1}:b{1} % does not throw an error.

Answer 2

[Sean de Wolski]

You should call the MATLAB module with a numeric input rather than a list. This is the data type conversion table. Use numeric types (probably matlab.double)

https://www.mathworks.com/help/releases/R2020b/matlab/matlab_external/pass-data-to-matlab-from-python.html

[Sean de Wolski]

This page is even more clear in exactly what you need to do:

https://www.mathworks.com/help/releases/R2020b/matlab/matlab_external/matlab-arrays-as-python-variables.html

Answer 3

[Jieqiang Wei]

I find this one is closest to what I am looking for, it seems the way I define the input variable in python manner directly is not a good option.

https://se.mathworks.com/matlabcentral/answers/437509-python-interface-to-matlab-runtime#comment_656434

[Sean de Wolski]

You seem to be finding the engine so that doesn't seem like the issue. You just need to cast the python data to a matlab double. The doc page I linked shows how to do this.