Rounding datetime to the nearest hour

Question

I have a question very similar to this one and this one but I'm stuck on some rounding issue.

I have a time series from a netCDF file and I'm trying to convert them to a datetime format. The format of the time series is in 'days since 1990-01-01 00:00:00'. Eventually I want output in the format .strftime('%Y%m%d.%H%M'). So for example I read my netCDF file as follows

import netCDF4
nc = netCDF4.Dataset(file_name)
time = np.array(nc['time'][:])

I then have

In [180]: time[0]
Out[180]: 365
In [181]: time[1]
Out[181]: 365.04166666651145

I then did

In [182]: start = datetime.datetime(1990,1,1)
In [183]: delta = datetime.timedelta(time[1])
In [184]: new_time = start + delta
In [185]: print(new_time.strftime('%Y%m%d.%H%M'))
19910101.0059

Is there a a way to "round" to the nearest hour so I get 19910101.0100?

Answer 1

You can round down with datetime.replace(), and round up by adding an hour to the rounded down value using datetime.timedelta(hours=1).

import datetime

def round_to_hour(dt):
    dt_start_of_hour = dt.replace(minute=0, second=0, microsecond=0)
    dt_half_hour = dt.replace(minute=30, second=0, microsecond=0)

    if dt >= dt_half_hour:
        # round up
        dt = dt_start_of_hour + datetime.timedelta(hours=1)
    else:
        # round down
        dt = dt_start_of_hour

    return dt

Note that since we're using replace the values we're not replacing (like the timezone - tzinfo) will be preserved.