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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 _adjust_font(self):
 """Ensure the font name is from our list and correctly spelled. """

        fnames = [k for k in Widget_fontdict.keys()]
        fl = list(map(str.lower, fnames))
        if (not self.text_font) or self.text_font.lower() not in fl:
            self.text_font = "helv"
        i = fl.index(self.text_font.lower())
        self.text_font = fnames[i]
        return