pythonタイムスタンプdatetime string変換

import datetime
import time

In [1]: now = datetime.datetime.now()
In [2]: time.mktime(now.timetuple())
Out[2]: 1433501775.0

In [3]: now.strftime('%Y-%m-%d')
Out[3]: '2015-06-05'

In [4]: type(now.strftime('%Y-%m-%d'))
Out[4]: str

In [5]: time_str = '2015-05-01 12:00:01'

In [5]: date_time = datetime.datetime.strptime(time_str,'%Y-%m-%d %H:%M:%S')

In [6]: date_time
Out[6]: datetime.datetime(2015, 5, 1, 12, 0, 1)

In [17]: time.strftime('%Y-%m-%d',time.localtime(aa))
Out[17]: '2015-06-05'