Fix: dataframe.loc int label could be warn

[dangjinghao]

According to the pandas document

A single label, e.g. 5 or 'a', (note that 5 is interpreted as a label of the index, and never as an integer position along the index).

dataframe.loc can accept int label, but for the previous stubs,df.loc[1] or similar codes would be warn.

[Dr-Irv]

Thanks @dangjinghao