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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 create_header(self, depth):
 """Create and return a widget that will be used as a header for the given depth Override this method if you want to have header widgets. The default implementation returns None. You can return None if you do not want a header for the given depth :param depth: the depth level :type depth: int :returns: a Widget that is used for the header or None :rtype: QtGui.QWidget|None :raises: None """

        if not (depth >= 0 and depth < len(self._headertexts)):
            return
        txt = self._headertexts[depth]
        if txt is None:
            return
        lbl = QtGui.QLabel(txt, self)
        return lbl