issue_comments: 388662640

It's confusing to me, because I don't see where NumPy is getting years or months metadata from the datetime.timedelta objects formed by np.diff(dates): In [12]: np.diff(dates) Out[12]: array([datetime.timedelta(31), datetime.timedelta(28), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(31), datetime.timedelta(28), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(31), datetime.timedelta(30), datetime.timedelta(31), datetime.timedelta(30)], dtype=object) Unlike np.timedelta64 objects, datetime.timedelta objects cannot be composed of units which have a varying length depending on the year (the coarsest internal resolution is days). The problem seems to occur only after calling np.unique; maybe the solution is to do the type conversion before calling np.unique? In [19]: np.unique(np.diff(dates).astype('timedelta64[ns]')) Out[19]: array([2419200000000000, 2592000000000000, 2678400000000000], dtype='timedelta64[ns]')