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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 list_functions(self, prefix=None):
 """List extant cloud functions."""

        return self.client.execute_command(
            'list',
            {'parent': "projects/{}/locations/{}".format(
                self.session.get_default_project(),
                self.region)}
        ).get('functions', [])