human
Complete this python program:
def _compute_signature(parameters, access_key_secret):
assistant
#Here is the Python program you requested.

    """Generate aliyun request signature
    """
    def percent_encode(line):
        if (not isinstance(line, six.string_types)):
            return line
        s = line
        if (sys.stdin.encoding is None):
            s = line.decode().encode('utf8')
        else:
            s = line.decode(sys.stdin.encoding).encode('utf8')
        res = _quote(s, '')
        res = res.replace('+', '%20')
        res = res.replace('*', '%2A')
        res = res.replace('%7E', '~')
        return res
    sortedParameters = sorted(list(parameters.items()), key=(lambda items: items[0]))
    canonicalizedQueryString = ''
    for (k, v) in sortedParameters:
        canonicalizedQueryString += ((('&' + percent_encode(k)) + '=') + percent_encode(v))
    stringToSign = ('GET&%2F&' + percent_encode(canonicalizedQueryString[1:]))
    h = hmac.new((access_key_secret + '&'), stringToSign, sha1)
    signature = base64.encodestring(h.digest()).strip()
    return signature