Dataframe.shape元组索引超出范围

Question

print "Boston housing dataset has {} data points with {} variables each.".format(df.shape)   

给出错误说＆＃34;元组索引超出范围＆＃34;

而

print "Boston housing dataset has {} data points with {} variables each.".format(*data.shape) 

正确输出数据框的维度。任何人都可以解释为什么会这样吗？