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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 is_valid(self):

 """Return True if all widget contents are valid"""

        for lineedit in self.lineedits:
            if lineedit in self.validate_data and lineedit.isEnabled():
                validator, invalid_msg = self.validate_data[lineedit]
                text = to_text_string(lineedit.text())
                if not validator(text):
                    QMessageBox.critical(self, self.get_name(),
                                     "%s:<br><b>%s</b>" % (invalid_msg, text),
                                     QMessageBox.Ok)
                    return False
        return True