为什么Pandas的DataFrame.apply方法在DataFrame为空时调用要应用的函数?例如:>>> df = pd.DataFrame({"foo": []})Empty DataFrame>>> x
[Series([], dtype: float64)] # <<< why was the
__init__(self): # have some extra attributes here that the pandas__getitem__(key)
# do some extra stuff here that the pandasDataFrame doesn't do but use the pandas method eventually