def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def update(self, dest, url, rev_options):
        # type: (str, HiddenText, RevOptions) -> None
        # First fetch changes from the default remote
        if self.get_git_version() >= parse_version('1.9.0'):
            # fetch tags in addition to everything else
            self.run_command(['fetch', '-q', '--tags'], cwd=dest)
        else:
            self.run_command(['fetch', '-q'], cwd=dest)
        # Then reset to wanted revision (maybe even origin/master)
        rev_options = self.resolve_revision(dest, url, rev_options)
        cmd_args = make_command('reset', '--hard', '-q', rev_options.to_args())
        self.run_command(cmd_args, cwd=dest)
        #: update submodules
        self.update_submodules(dest)