[SciPy-user] Changes in SVN scipy_core
oliphant.travis at ieee.org
Wed Dec 14 16:56:26 CST 2005
It's great to see the configuration stuff getting better in
scipy.distutils. Thanks to Pearu for all his hard work on
I want to let you all know about the recent changes in the SVN version
of scipy_core. As you may recall, I dramatically improved the way the
data in an array can be understood by improving the PyArray_Descr
structure and making it an object. As part of that improvement, it
became clear that the NOTSWAPPED flag was an anomaly and shouldn't be a
flag on the array itself. The byte-order of the data is a property of
the data-type descriptor. This is especially clear when considering
records which according to the array protocol can have some fields in
one byte order and some in another.
As a result, I've removed the NOTSWAPPED flag from the array object.
The equivalent of arr.flags.notswapped is now arr.dtypedescr.isnative.
In C, the macro PyArray_ISNOTSWAPPED(arr) is still available but it
checks the data-type descriptor. All C-API and python calls that used to
pass a swap paramter along with a data-type descriptor have the swap
These C-API changes mean you will need to fully rebuild (remove the
build directory and build) both scipy_core and scipy if you check out
the new SVN version. I realize that the pace of development has been
rapid --- but I'm on a tight schedule ;-) Hopefully, this wil be the
last relatively major change to the code base for a while.
All tests pass for me for full scipy after these changes. As we all
know, however, there still may be remaining issues. One issue, for
example, is that a.copy() returns a copy of the data (with the same
data-type descriptor so no change in the byte-order is done).
There is a new method
which returns the equivalent of
which returns a new view of the data using a different byte-order
Note that the newbyteorder method of a dtypedescr object returns a new
copy of the dtypedescr object with the byte-orders swapped if <arg> is
not given or forces the byteorder to a particular value if arg is given
(and not arg=='|' which means ignore). All fields of the dtypedescr
object are (recursively) updated with the same rule as well.
Look what comes along for the ride because of these changes:
a = ones((5,), '<i4') # define a little-endian array
b = ones((5,), '>i4') # define a big-endian array
You can use these byte-order flags anywhere a data-type descriptor
(dtype parameter) is required. I have not tested all the possibilities,
of course, so there may still be outstanding issues.
Note, however, that if you work with arrays that are not in native-byte
order some operations will generally be slower.
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