<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def checkout(self, branch_name):

 """ Checkout a branch by name. """

        try:
            find(
                self.repo.branches, lambda b: b.name == branch_name
            ).checkout()
        except OrigCheckoutError as e:
            raise CheckoutError(branch_name, details=e)