[Numpy-discussion] Assigning complex values to a real array

Ryan May rmay31@gmail....
Tue Dec 8 08:23:24 CST 2009

>> At a minimum, this inconsistency needs to be cleared up.  My
>> preference
>> would be that the programmer should have to explicitly downcast from
>> complex to float, and that if he/she fails to do this, that an
>> exception be
>> triggered.
> That would most likely break a *lot* of deployed code that depends on
> the implicit downcast behaviour. A less harmful solution (if a
> solution is warranted, which is for the Council of the Elders to
> decide) would be to treat the Python complex type as a special case,
> so that the .real attribute is accessed instead of trying to cast to
> float.

Except that the exception raised on downcast is the behavior we really
want.  We don't need python complex types introducing subtle bugs as

I understand why we have the silent downcast from complex to float,
but I consider it a wart, not a feature.  I've lost hours tracking
down bugs where I'm putting complex data from some routine into a new
array (without specifying a dtype) ends up with the complex downcast
silently to float64. The only reason you even notice it is because at
the end you have incorrect answers. I know to look for it now, but for
inexperienced users, it's a pain.


Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma

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