'Return True if all widget contents are valid'

def is_valid(self):

    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
