A dialog to get a file name.
    The "default" argument specifies a file path.

    save=False -> file for loading
    save=True -> file for saving

    Return the file path that the user entered, or None if he cancels the operation.

    :param message: message to be displayed.
    :param save: bool 0 -> load , 1 -> save
    :param title: window title
    :param default: default file path
    :rtype: None or string

def ask_file(message='Select file for open.', default='', title='', save=False):
    """
    A dialog to get a file name.
    The "default" argument specifies a file path.

    save=False -> file for loading
    save=True -> file for saving

    Return the file path that the user entered, or None if he cancels the operation.

    :param message: message to be displayed.
    :param save: bool 0 -> load , 1 -> save
    :param title: window title
    :param default: default file path
    :rtype: None or string
    """
    return backend_api.opendialog("ask_file", dict(message=message, default=default, title=title, save=save))