df[['var1','var2']] = df[['var1','var2']].applymap("{0:.2f}".format)
    等效于
    df[['var1','var2']].apply(lambda x: map(lambda x:'{:.2f}%'.format(x),x),axis=1)

    df['var3'] = df['var3'].applymap(lambda x: "{0:.2f}%".format(x*100))