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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 _render_item(self, dstack, key, value = None, **settings):
 """ Format single tree line. """

        cur_depth = len(dstack) - 1

        treeptrn = ''
        s = self._es_text(settings, settings[self.SETTING_TREE_FORMATING])
        for ds in dstack:
            treeptrn += ' ' + self.fmt_text(self.tchar(settings[self.SETTING_TREE_STYLE], cur_depth, *ds), **s) + ''

        strptrn = "{}"
        if value is not None:
            strptrn += ": {}"
        s = self._es_text(settings, settings[self.SETTING_TEXT_FORMATING])
        strptrn = self.fmt_text(strptrn.format(key, value), **s)

        return '{} {}'.format(treeptrn, strptrn)