really_removed = set()

        for p in parents:

            for node in self.removed:

                try:

                    p.get_node(node.path)

                    really_removed.add(node)

                except ChangesetError:

                    pass

        not_removed = set(self.removed) - really_removed

        if not_removed:

            raise NodeDoesNotExistError("Cannot remove node at %s from "

                "following parents: %s" % (not_removed[0], parents))

    def commit(self, message, author, parents=None, branch=None, date=None,

            **kwargs):

        """

        Performs in-memory commit (doesn't check workdir in any way) and

        returns newly created ``Changeset``. Updates repository's

        ``revisions``.

        .. note::

            While overriding this method each backend's should call

            ``self.check_integrity(parents)`` in the first place.

        :param message: message of the commit

        :param author: full username, i.e. "Joe Doe <joe.doe@example.com>"

        :param parents: single parent or sequence of parents from which commit

          would be derived

        :param date: ``datetime.datetime`` instance. Defaults to

          ``datetime.datetime.now()``.

        :param branch: branch name, as string. If none given, default backend's

          branch would be used.

        :raises ``CommitError``: if any error occurs while committing

        """

        raise NotImplementedError

class EmptyChangeset(BaseChangeset):

    """

    An dummy empty changeset. It's possible to pass hash when creating

    an EmptyChangeset

    """

    def __init__(self, cs='0' * 40, repo=None, requested_revision=None,

                 alias=None, revision=-1, message='', author='', date=None):

        self._empty_cs = cs

        self.revision = revision

        self.message = message

        self.author = author

        self.date = date or datetime.datetime.fromtimestamp(0)

        self.repository = repo

        self.requested_revision = requested_revision

        self.alias = alias

    @LazyProperty

    def raw_id(self):

        """

        Returns raw string identifying this changeset, useful for web

        representation.

        """

        return self._empty_cs

    @LazyProperty

    def branch(self):

        from kallithea.lib.vcs.backends import get_backend

        return get_backend(self.alias).DEFAULT_BRANCH_NAME

    @LazyProperty

    def short_id(self):

        return self.raw_id[:12]

    def get_file_changeset(self, path):

        return self

    def get_file_content(self, path):

        return u''

    def get_file_size(self, path):

        return 0

class CollectionGenerator(object):

    def __init__(self, repo, revs):

        self.repo = repo

        self.revs = revs

    def __len__(self):

        return len(self.revs)

    def __iter__(self):

        for rev in self.revs:

            yield self.repo.get_changeset(rev)

    def __repr__(self):

        return '<CollectionGenerator[len:%s]>' % (len(self))