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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 get_branches(self, repo_slug=None):
 """ Get a single repository on Bitbucket and return its branches."""

        repo_slug = repo_slug or self.repo_slug or ''
        url = self.url('GET_BRANCHES',
                       username=self.username,
                       repo_slug=repo_slug)
        return self.dispatch('GET', url, auth=self.auth)