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 save(self, verbosity=1, *args, **kwargs):
        connection = connections[get_tenant_database_alias()]
        is_new = self.pk is None
        has_schema = hasattr(connection, 'schema_name')
        if has_schema and is_new and connection.schema_name != get_public_schema_name():
            raise Exception("Can't create tenant outside the public schema. "
                            "Current schema is %s." % connection.schema_name)
        elif has_schema and not is_new and connection.schema_name not in (self.schema_name, get_public_schema_name()):
            raise Exception("Can't update tenant outside it's own schema or "
                            "the public schema. Current schema is %s."
                            % connection.schema_name)

        super().save(*args, **kwargs)

        if has_schema and is_new and self.auto_create_schema:
            try:
                self.create_schema(check_if_exists=True, verbosity=verbosity)
                post_schema_sync.send(sender=TenantMixin, tenant=self.serializable_fields())
            except Exception:
                # We failed creating the tenant, delete what we created and
                # re-raise the exception
                self.delete(force_drop=True)
                raise
        elif is_new:
            # although we are not using the schema functions directly, the signal might be registered by a listener
            schema_needs_to_be_sync.send(sender=TenantMixin, tenant=self.serializable_fields())
        elif not is_new and self.auto_create_schema and not schema_exists(self.schema_name):
            # Create schemas for existing models, deleting only the schema on failure
            try:
                self.create_schema(check_if_exists=True, verbosity=verbosity)
                post_schema_sync.send(sender=TenantMixin, tenant=self.serializable_fields())
            except Exception:
                # We failed creating the schema, delete what we created and
                # re-raise the exception
                self._drop_schema()
                raise