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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 metric_descriptor_path(cls, project, metric_descriptor):
 """Return a fully-qualified metric_descriptor string."""

        return google.api_core.path_template.expand(
            "projects/{project}/metricDescriptors/{metric_descriptor=**}",
            project=project,
            metric_descriptor=metric_descriptor,
        )