Fix floating point precision errors in netCDF time variables

change.py

import numpy as np
import netCDF4 as nc4
from datetime import datetime, timdelta

def round_date_time(dt, round_seconds=60):
    """
    modified from: http://stackoverflow.com/questions/3463930/how-to-round-the-minute-of-a-datetime-object-python

    Round a datetime object to any time laps in seconds, return the
    timedelta to add to the datetime to round it.

    dt : datetime object
    round_seconds : Closest number of seconds to round to, default 1 minute.
    """
    seconds = (dt - dt.min).seconds
    # '//' is a floor division
    rounding = (seconds + round_seconds/2) // round_seconds * round_seconds
    return timedelta(0, rounding - seconds, -dt.microsecond)
    
tvar = nc.variables['time']
tvard = tvar[:]

dts = nc4.num2date(tvard,
                   units=tvar.units,
                   calendar=getattr(tvar, 'calendar', 'standard'))
add_seconds = np.vectorize(lambda x: round_date_time(x, 60))
tvar[:] = nc4.date2num(dts + add_seconds(dts),
                       units=tvar.units,
                       calendar=getattr(tvar, 'calendar', 'standard'))