Dump model into a text file.

        Parameters
        ----------
        foout : string
            Output file name.
        fmap : string, optional
            Name of the file containing feature map names.
        with_stats : bool (optional)
            Controls whether the split statistics are output.

def dump_model(self, fout, fmap='', with_stats=False):
        """
        Dump model into a text file.

        Parameters
        ----------
        foout : string
            Output file name.
        fmap : string, optional
            Name of the file containing feature map names.
        with_stats : bool (optional)
            Controls whether the split statistics are output.
        """
        if isinstance(fout, STRING_TYPES):
            fout = open(fout, 'w')
            need_close = True
        else:
            need_close = False
        ret = self.get_dump(fmap, with_stats)
        for i in range(len(ret)):
            fout.write('booster[{}]:\n'.format(i))
            fout.write(ret[i])
        if need_close:
            fout.close()