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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 G_calc(item1, item2):
 """ Calculate G-measure & G-mean. :param item1: PPV or TPR or TNR :type item1 : float :param item2: PPV or TPR or TNR :type item2 : float :return: G-measure or G-mean as float """

    try:
        result = math.sqrt(item1 * item2)
        return result
    except Exception:
        return "None"