If you want to format a datetime object in a specific format that is different from the standard format, it’s best to explicitly specify that format:
>>> import datetime
>>> datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
'2011-11-03 18:21:26'
See the documentation of datetime.strftime() for an explanation of the % directives.
Starting from Python 3.6, the isoformat() method is flexible enough to also produce this format:
datetime.datetime.now().isoformat(sep=" ", timespec="seconds")