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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fitter(self, n=0, ftype="real", colfac=1.0e-8, lmfac=1.0e-3):
 """Create a sub-fitter. The created sub-fitter can be used in the same way as a fitter default fitter. This function returns an identification, which has to be used in the `fid` argument of subsequent calls. The call can specify the standard constructor arguments (`n`, `type`, `colfac`, `lmfac`), or can specify them later in a :meth:`set` statement. :param n: number of unknowns :param ftype: type of solution Allowed: real, complex, separable, asreal, conjugate :param colfac: collinearity factor :param lmfac: Levenberg-Marquardt factor :param fid: the id of a sub-fitter """

        fid = self._fitproxy.getid()
        ftype = self._gettype(ftype)
        n = len(self._fitids)
        if 0 <= fid < n:
            self._fitids[fid] = {}
        elif fid == n:
            self._fitids.append({})
        else:
            # shouldn't happen
            raise RangeError("fit id out of range")
        self.init(n=n, ftype=ftype, colfac=colfac, lmfac=lmfac, fid=fid)
        return fid