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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 url(self):
 """The fetching target URL. The default behavior of this property is build URL string with the :const:`~brownant.dinergate.Dinergate.URL_TEMPLATE`. The subclasses could override :const:`~brownant.dinergate.Dinergate.URL_TEMPLATE` or use a different implementation. """

        if not self.URL_TEMPLATE:
            raise NotImplementedError
        return self.URL_TEMPLATE.format(self=self)