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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 create_branch(self, branch_name: str):
 """ Creates a new branch Args: branch_name: name of the branch """

        LOGGER.info('creating branch: %s', branch_name)
        self._validate_branch_name(branch_name)
        if branch_name in self.list_branches():
            LOGGER.error('branch already exists')
            sys.exit(-1)
        new_branch = self.repo.create_head(branch_name)
        new_branch.commit = self.repo.head.commit