def secure_filename(filename):
    r"""Borrowed from :mod:`werkzeug.utils`, under the BSD 3-clause license.

    Pass it a filename and it will return a secure version of it.  This
    filename can then safely be stored on a regular file system and passed
    to :func:`os.path.join`.  The filename returned is an ASCII only string
    for maximum portability.

    On windows systems the function also makes sure that the file is not
    named after one of the special device files.

    >>> secure_filename("My cool movie.mov")
    'My_cool_movie.mov'
    >>> secure_filename("../../../etc/passwd")
    'etc_passwd'
    >>> secure_filename(u'i contain cool \xfcml\xe4uts.txt')
    'i_contain_cool_umlauts.txt'

    The function might return an empty filename.  It's your responsibility
    to ensure that the filename is unique and that you generate random
    filename if the function returned an empty one.

    :param filename: the filename to secure
    """
    _filename_ascii_strip_re = re.compile(r'[^A-Za-z0-9_.-]')
    _windows_device_files = ('CON', 'AUX', 'COM1', 'COM2', 'COM3', 'COM4',
                             'LPT1', 'LPT2', 'LPT3', 'PRN', 'NUL')
    if isinstance(filename, text_type):
        from unicodedata import normalize
        filename = normalize('NFKD', filename).encode('ascii', 'ignore')
        if not PY2:
            filename = filename.decode('ascii')
    for sep in os.path.sep, os.path.altsep:
        if sep:
            filename = filename.replace(sep, ' ')
    filename = str(_filename_ascii_strip_re.sub('', '_'.join(
                   filename.split()))).strip('._')

    # on nt a couple of special files are present in each folder.  We
    # have to ensure that the target file is not such a filename.  In
    # this case we prepend an underline
    if os.name == 'nt' and filename and \
       filename.split('.')[0].upper() in _windows_device_files:
        filename = '_' + filename

    return filename
def db_sync(engine, abs_path, version=None, init_version=0, sanity_check=True):
    """Upgrade or downgrade a database.

    Function runs the upgrade() or downgrade() functions in change scripts.

    :param engine:       SQLAlchemy engine instance for a given database
    :param abs_path:     Absolute path to migrate repository.
    :param version:      Database will upgrade/downgrade until this version.
                         If None - database will update to the latest
                         available version.
    :param init_version: Initial database version
    :param sanity_check: Require schema sanity checking for all tables
    """

    if version is not None:
        try:
            version = int(version)
        except ValueError:
            raise exception.DbMigrationError(
                message=_("version should be an integer"))

    current_version = db_version(engine, abs_path, init_version)
    repository = _find_migrate_repo(abs_path)
    if sanity_check:
        _db_schema_sanity_check(engine)
    if version is None or version > current_version:
        return versioning_api.upgrade(engine, repository, version)
    else:
        return versioning_api.downgrade(engine, repository,
                                        version)