code: def checkout(self, revision=None, clean=False):
          
          # 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))
docs: 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.