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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 do_work_on(self, repo):
        '''
        Make repo the active one.
        Commands working on a repo will use it as default for repo parameter.
        '''
        self.abort_on_nonexisting_repo(repo, 'work_on')
        self.network.active_repo = repo