Given you want to round down to the hour, you can simply replace microsecond, second and minute with zeros:
print(datetime.now().replace(microsecond=0, second=0, minute=0))
If you want to round down to the previous hour (as stated in the example 2017-01-11 13:26:12.0 to 2017-01-11 12:00:00.0), replace microsecond, second and minute with zeros, then subtract one hour:
from datetime import datetime, timedelta
print(datetime.now().replace(microsecond=0, second=0, minute=0) - timedelta(hours=1))
Example in the shell:
$ python3
Python 3.5.2 (default, Nov 17 2016, 17:05:23)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from datetime import datetime, timedelta
>>> print(datetime.now().replace(microsecond=0, second=0, minute=0) - timedelta(hours=1))
2017-01-11 16:00:00