I have a userdefined numpy type for mx.DateTime and one for mx.DateTimeDelta. Info on these packages is available here (http://www.egenix.com/files/python/eGenix-mx-Extensions.html). In any case most things work. What I am left with is three problems: 1. I cannot figure out how to cleanly or even at all, get type detection to work So this works: In [35]: numpy.array([D('2002-01-02 00:00:00.00'), D('2002-01-03 00:00:00.00')], dtype=numpy.mxDateTimeType) Out[35]: array([2002-01-02 00:00:00.00, 2002-01-03 00:00:00.00], dtype=mxNumpyDateTime) But this doesn't: In [36]: numpy.array([D('2002-01-02 00:00:00.00'), D('2002-01-03 00:00:00.00')]) Out[36]: array([2002-01-02 00:00:00.00, 2002-01-03 00:00:00.00], dtype=object) I.e. if I don't specify the type it gives me an object dtype. This is unlike the behavior for strings, ints, etc. I think I know where the C code is that controls this but it is not obvious to me how to change it without making it dependent on mx.DateTime at compile time or having to put a bunch of #define #ifdef magic around it. It would be preferable to figure out a way to specify autodetection, from the outside, so to speak. 2. I can get printing to work but only using a quasi hack in the numpy arrayprint.py code. It works with or without presense of the mx libraries but doesn't seem to me entirely clean. 3. Broadcasting has bugs. See example below: The basic case (2,) - (2,) arrays works. In [37]: numpy.array([D('2002-01-02 00:00:00.00'), D('2002-01-03 00:00:00.00')], dtype=numpy.mxDateTimeType) - numpy.array([DateTime.DateTimeDeltaFromDays(1)], dtype=numpy.mxDateTimeDeltaType) Out[37]: array([2002-01-01 00:00:00.00, 2002-01-02 00:00:00.00], dtype=mxNumpyDateTime) The broadcasting case of (2,) - (1,) works: In [39]: numpy.array([D('2002-01-02 00:00:00.00'), D('2002-01-03 00:00:00.00')], dtype=numpy.mxDateTimeType) - numpy.array([DateTime.DateTimeDeltaFromDays(20)], dtype=numpy.mxDateTimeDeltaType) Out[39]: array([2001-12-13 00:00:00.00, 2001-12-14 00:00:00.00], dtype=mxNumpyDateTime) The extremely similar (2,) - () array: In [40]: numpy.array([D('2002-01-02 00:00:00.00'), D('2002-01-03 00:00:00.00')], dtype=numpy.mxDateTimeType) - numpy.array(DateTime.DateTimeDeltaFromDays(20), dtype=numpy.mxDateTimeDeltaType) --------------------------------------------------------------------------- <type 'exceptions.TypeError'> Traceback (most recent call last) /home/tom/src/<ipython console> in <module>() <type 'exceptions.TypeError'>: function not supported for these types, and can't coerce safely to supported types Finally the (2,) - scalar doesn't work either: In [41]: numpy.array([D('2002-01-02 00:00:00.00'), D('2002-01-03 00:00:00.00')], dtype=numpy.mxDateTimeType) - DateTime.DateTimeDeltaFromDays(20) --------------------------------------------------------------------------- <type 'exceptions.TypeError'> Traceback (most recent call last) /home/tom/src/<ipython console> in <module>() <type 'exceptions.TypeError'>: function not supported for these types, and can't coerce safely to supported types The final one might not work even if broadcasting worked properly simply because of the autodetection problem listed in 2. The (2,) - (), however, should work, I would think, because it has the type explicitly set. --Tom