In [1]: import datetime

In [2]: dti = pd.to_datetime(
   ...:     ["1/1/2018", np.datetime64("2018-01-01"), datetime.datetime(2018, 1, 1)]
   ...: )
   ...: 

In [3]: dti
Out[3]: DatetimeIndex(['2018-01-01', '2018-01-01', '2018-01-01'], dtype='datetime64[ns]', freq=None)