Numpy: Checking if a value is NaT

pandas can check for NaT with pandas.isnull:

>>> import numpy as np
>>> import pandas as pd
>>> pd.isnull(np.datetime64('NaT'))
True

If you don’t want to use pandas you can also define your own function (parts are taken from the pandas source):

nat_as_integer = np.datetime64('NAT').view('i8')

def isnat(your_datetime):
    dtype_string = str(your_datetime.dtype)
    if 'datetime64' in dtype_string or 'timedelta64' in dtype_string:
        return your_datetime.view('i8') == nat_as_integer
    return False  # it can't be a NaT if it's not a dateime

This correctly identifies NaT values:

>>> isnat(np.datetime64('NAT'))
True

>>> isnat(np.timedelta64('NAT'))
True

And realizes if it’s not a datetime or timedelta:

>>> isnat(np.timedelta64('NAT').view('i8'))
False

In the future there might be an isnat-function in the numpy code, at least they have a (currently open) pull request about it: Link to the PR (NumPy github)