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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 set_custom_value(self, key, value):
 """Set one custom parameter with the given value. We assume that the list of custom parameters does not already contain the given parameter so we only append. """

        self._owner.customParameters.append(
            self._glyphs_module.GSCustomParameter(name=key, value=value)
        )