Convert regex pattern to string.

    If pattern is string it returns itself,
    if pattern is SRE_Pattern then return pattern attribute
    :param pattern: pattern object or string
    :return: str: pattern sttring

def pattern_to_str(pattern):
    """Convert regex pattern to string.

    If pattern is string it returns itself,
    if pattern is SRE_Pattern then return pattern attribute
    :param pattern: pattern object or string
    :return: str: pattern sttring
    """
    if isinstance(pattern, str):
        return repr(pattern)
    else:
        return repr(pattern.pattern) if pattern else None