human
Complete this python program:
def _normalize_answer(s):
assistant
#Here is the Python code you requested.

    """Lower text and remove punctuation, articles and extra whitespace.
    """
    def remove_articles(text):
        return re_art.sub('    ', text)
    def white_space_fix(text):
        return '    '.join(text.split())
    def remove_punc(text):
        text = re_punc.sub('    ', text)
        exclude = set("_'")
        return ''.join((ch for ch in text if (ch not in exclude)))
    def lower(text):
        return text.lower()
    return white_space_fix(remove_articles(remove_punc(lower(s))))