Compute the Mann-Whitney U test for unequal group sample sizes.

def print_MannWhitneyU(div_calc):
    """
    Compute the Mann-Whitney U test for unequal group sample sizes.
    """
    try:
        x = div_calc.values()[0].values()
        y = div_calc.values()[1].values()
    except:
        return "Error setting up input arrays for Mann-Whitney U Test. Skipping "\
               "significance testing."
    T, p = stats.mannwhitneyu(x, y)
    print "\nMann-Whitney U test statistic:", T
    print "Two-tailed p-value: {}".format(2 * p)