python class ‘str‘ 字符串转换为 class ‘pandas._libs.tslibs.timestamps.Timestamp‘时间戳

>>> import pandas as pd
>>> pd.to_datetime('2021-02-17')
Timestamp('2021-02-17 00:00:00')
>>> type('2021-02-17')
<class 'str'>
>>> type(pd.to_datetime('2021-02-17'))
<class 'pandas._libs.tslibs.timestamps.Timestamp'>