Wrapper for a file-communicating objective function

"""Code to optimize an objective function that can be called in the
system shell and communicates via files.
"""

import subprocess
import cma  # pip install cma

def _tf_write(x):
    """transformation before to write parameters"""
    return repr(list(x))

class FitnessViaFilesWrapper:
    """wrap an objective function that uses files to read the input variables
    and write the output value
    """
    def __init__(self, fun, filename_params, filename_res,
                 tf_write=_tf_write, tf_read=float):
        """`fun` reads from `filename_params` and writes to `filename_res`"""
        self.fun = fun
        self.filename_params = filename_params
        self.filename_res = filename_res
        self.tf_write = tf_write
        self.tf_read = tf_read
    def __call__(self, x):
        """objective function call.

        Write ``tf_write(x)`` to file and call `self.fun` and
        return content of `self.filename_res` transformed by
        `tf_read`.
        """
        with open(self.filename_params, 'wt') as f:
            f.write(self.tf_write(x))
        self.fun()  # writes into file self.filename_res
        with open(self.filename_res, 'rt') as f:
            res = self.tf_read(f.read())
        return res

def call_matlab():
    """objective function that uses the files '_in' and '_out'"""
    # subprocess.call('matlab -nodisplay -nodesktop -nojvm -nosplash < simulink-script _in _traject ...', shell=True)
    # here we may want to compute the deviation of _traject from the desired trajectory
    # and write the error to be minimized to _out

    # testing example:
    import ast
    with open('_in', 'rt') as f:
        x = ast.literal_eval(f.read())
    fun_val = cma.ff.elli(x)
    with open('_out', 'wt') as f:
        f.write(repr(fun_val))

f = FitnessViaFilesWrapper(call_matlab, '_in', '_out')
# f = cma.ff.elli

# testing the code, try to find minimizer of f
x, es = cma.fmin2(f, 3 * [1], 1);