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