python两个日期，求间隔的天数

>>> from datetime import date

>>> delta = date.today() - date(2017,1,1)

>>> delta.days
387

>>> import pandas as pd
>>> t1 = pd.to_datetime('2017-10-01')
>>> t2 = pd.to_datetime('2018-02-01')
>>> (t2 - t1).days
123