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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pct_decode(s):
 """ Return the percent-decoded version of string s. 'Coucou, je suis convivial' '' '%25' """

    if s is None:
        return None
    elif not isinstance(s, unicode):
        s = str(s)
    else:
        s = s.encode('utf8')

    return PERCENT_CODE_SUB(lambda mo: chr(int(mo.group(0)[1:], 16)), s)