On Sun, Jul 20, 2008 at 10:41 PM, Charles R Harris < charlesr.harris@gmail.com> wrote:
On Sun, Jul 20, 2008 at 8:32 PM, Timothy Hochberg <tim.hochberg@ieee.org> wrote:
On Sun, Jul 20, 2008 at 3:47 PM, Robert Kern <robert.kern@gmail.com> wrote:
On Sun, Jul 20, 2008 at 17:42, Charles R Harris <charlesr.harris@gmail.com> wrote:
Hi All,
I "fixed" ticket #754, but it leads to a ton of problems. The original discussion is here. The problems that arise come from conversion to different types.
In [26]: a Out[26]: array([ Inf, -Inf, NaN, 0., 3., -3.])
In [27]: sign(a).astype(int) Out[27]: array([ 1, -1, -2147483648, 0, 1, -1])
In [28]: sign(a).astype(bool) Out[28]: array([ True, True, True, False, True, True], dtype=bool)
In [29]: sign(a) Out[29]: array([ 1., -1., NaN, 0., 1., -1.])
In [30]: bool(NaN) Out[30]: True
So there are problems with at minimum the following.
1) The way NaN is converted to bool. I think it should be False.
It's not really our choice. That's Python's bool(). For the things that are our choice (e.g. array([nan]).astype(bool)) I think we should stay consistent with Python.
<DELURK>
I agree that this is a good goal. However, in the past, Python's treatment of NaNs has been rather platform dependent and add hock. In this case, I suspect that you are OK since the section "Truth Value Testing" in the Python docs is pretty clear that any non-zero value of a numerical type is True.
However...
2) The way NaN is converted to int types. I think it should be 0.
I agree. That's what int(nan) gives:
int(nan) 0L
This is GvR in http://mail.python.org/pipermail/python-dev/2008-January/075865.html:
Well, now, that opens a whole other bag of toasted scorpions.
It looks like long(inf) and int(inf) already raise OverflowError and
that should stay.
In [3]: (ones(2)*float(inf)).astype(int8) Out[3]: array([0, 0], dtype=int8)
In [4]: (ones(2)*float(inf)).astype(int32)
Out[4]: array([-2147483648, -2147483648])
In [5]: (ones(2)*float(inf)).astype(int64) Out[5]: array([-9223372036854775808, -9223372036854775808], dtype=int64)
Also, In [8]: (ones(2)*float(inf)).astype(uint8) Out[8]: array([0, 0], dtype=uint8) In [9]: (ones(2)*float(inf)).astype(uint16) Out[9]: array([0, 0], dtype=uint16) In [10]: (ones(2)*float(inf)).astype(uint32) Out[10]: array([0, 0], dtype=uint32) In [11]: (ones(2)*float(inf)).astype(uint64) Out[11]: array([0, 0], dtype=uint64) Chuck