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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 _lock_aspect_cb(self, w, tf):
 """This function is called when the user clicks the 'Lock aspect' checkbox. `tf` is True if checked, False otherwise. """

        self._lock_aspect = tf
        self.w.aspect.set_enabled(tf)
        if self._lock_aspect:
            self._set_aspect_cb()
        else:
            wd, ht = self.get_wdht()
            _as = self.calc_aspect_str(wd, ht)
            self.w.aspect.set_text(_as)