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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 checkout(self, revision=None, clean=False):
 """ Update the working tree of the local repository to the specified revision. :param revision: The revision to check out (a string, defaults to :attr:`default_revision`). :param clean: :data:`True` to discard changes in the working tree, :data:`False` otherwise. """

        # Make sure the local repository exists and supports a working tree.
        self.create()
        self.ensure_working_tree()
        # Update the working tree of the local repository.
        revision = revision or self.default_revision
        logger.info("Checking out revision '%s' in %s ..", revision, format_path(self.local))
        self.context.execute(*self.get_checkout_command(revision, clean))