def get_filenames(root, prefix=u'', suffix=u''):
    """Function for listing filenames with given prefix and suffix in the root directory.
    
    Parameters
    ----------
    
    prefix: str
        The prefix of the required files.
    suffix: str
        The suffix of the required files
        
    Returns
    -------
    list of str
        List of filenames matching the prefix and suffix criteria.
    """
    return [fnm for fnm in os.listdir(root) if fnm.startswith(prefix) and fnm.endswith(suffix)]