Example of creating a new fitter

newfitter.py

from astropy.models.fitting import Fitter
import numpy as np
from scipy import optimize

class SLSQPFitter(Fitter):
    def __init__(self):
        super().__init__(optimizer=SLSQP, statistic=leastsquare)
                             
    def errorfunc(self, fps, *args):
        model = args[0]
        meas = args[-1]
        model.parameters = fps
        res = model(*args[1:-1]) - meas
        return np.sum(res**2)
         
    def __call__(self, model, x, y , maxiter=100, epsilon=10**(-12)):
        model_copy = model.copy()
        b = [model.bounds[key] for key in model.param_names]
        fitpars = optimize.fmin_slsqp(self.errorfunc, x0=model_copy.parameters[:],
            args=(model_copy, x,y), bounds=b)
        model_copy.parameters = fitpars
        return model_copy