[Python-Dev] Bool type and arrays

[Guido van Rossum]

> Guido said not to "mix up" the question of bit arrays with the bool
> proposal, but really, they *are* mixed up. The minute there is a bool
> type in Python people will be able to make Numeric arrays (not to
> mention Python arrays) with elements of type "bool".

I dunno about Numeric, but you cannot use an arbitrary type for the
'array' module -- you must use one of the documented codes that tell
the array module what size items to use.  Since there's no code
(documented or otherwise) that refers to bool, you *won't* be able to
create bool arrays with the array module.

I thought Numeric used a similar scheme?

> They will then be
> annoyed to learn that they are making arrays of objects and the result
> is a big array, not a small array, and that they would have been better
> off with our byte integer arrays. Depending on the implementation,
> mixing in bool values in a list of integers might persuade Numeric's
> array constructor to make them all objects.

I made bool a subclass of int to minimize this danger, but I don't
know whether Numeric uses PyInt_Check() or not.  If it uses that
macro, it should be safe.

> In short, they are mixed up in the sense that this proposed intellectual
> nicety will cause us Nummies a lot of grief. Not that you aren't allowed
> to give us grief, like you did with the "true division", but I wanted
> people to know they would be inflicting pain.

But let's not worry about pain we don't know that we'll really be
experiencing.  I like to look at things from the bright side.

Wait until I check it into CVS next week. :-)

> BTW: There is quite a bit of pent-up demand in the Numeric community for
> bit arrays. However, nobody knows how to do it since the internal Numpy
> structures use a byte as the atomic unit of addressing. 

Same for the Python array module.

--Guido van Rossum (home page: http://www.python.org/~guido/)