How to pass a dict as argument in a called matlab function from Python

Question

I'm making a soft that call matlab functions, and i want to pass a dict as argument in a matlab function using matlab.engine in python.

Like this:

def Parametrize(confFile):
    """ Return

    Argument:
    confFile    --  str()   Configuration File path

    Function that call MatLab function passing handles structure/dict as
    argument. The return value of MatLab function called Parametrize(handles)
    is the modified handles structure.
    """
    print("ouai")
    test = dict()
    keys = range(4)
    values = ["Hi", "I", "am", "John"]
    for i in keys:
        test[str(i)] = values[i]
    eng = matlab.engine.start_matlab()
    eng.addpath(vssFolderPath)
    res = eng.Transit(test)
    print(type(res))
    print(res)

And the matlab function is pretty basic i'm testing how to pass data from Python to Matlab:

function a = Transit(test)
field = 'Value1';
value = {'TEST'};
disp(test)
a = struct(field,value);

i always have this error :

ValueError: invalid field for MATLAB struct

But i read this document that explain how to pass data from python to matlab and i don't know why it's not working for me.

Azim J · Accepted Answer · 2019-09-29 18:32:46Z

3

The documentation says:

That is passing a dictionary to MATLAB is not supported if your keys are numeric. I think this would also apply to numbers converted to strings. From your code it looks like your dictionary is:

test={'0':'Hi','1':'I','2':'am','3':'John'}

Here the keys, although strings, are numbers [0-9].

Field-names in MATLAB cannot start with a numeric character [0-9] (matlab.lang.makeValidName). Try changing the keys to start with an alphabetic character [a-zA-Z]. In your case, it is seems that MATLAB is trying to create field-names from your keys and failing because the field-names start with a number which MATLAB does not support as per the docs.

edited Sep 29, 2019 at 18:32

answered Aug 12, 2019 at 16:28

Azim J

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1 Comment

Azim J Over a year ago

@PAYREQuentin your most welcome. I'm glad it worked.

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