您似乎在Excel中验证数据-原始日期已更改.

It looks like you verify data in Excel - original dates are changed.

尝试使用某些文本编辑器，例如Notepad++-csv文件数据正确.

Try some text editor like Notepad++ - csv file data are correct.

如果使用默认选项:

print (df.head().to_csv())
date,price_am,price_pm
2017-06-01,E,E
2017-06-02,D,E
2017-06-03,C,D