On Mon, May 21, 2012 at 4:37 PM, Travis Oliphant <tra...@continuum.io> wrote: > This is the right place to ask, it's just that it can take time to get an > answer because people who might know the answer may not have the time to > respond immediately. > > The short answer is that this is not really a "normal" bug, but it could be > considered a "design" bug (although the issues may not be straightforward to > resolve). What that means is that it may not be changed in the short term > --- and you should just use the first spelling. > > Structured arrays can be a confusing area of NumPy for several of reasons. > You've constructed an example that touches on several of them. You have a > data-type that is a "structure" array with one member ("tuple"). That > member contains a 2-vector of integers. > > First of all, it is important to remember that with Python, doing > a['tuple'][0] = (1,2) is equivalent to b = a['tuple']; b[0] = (1,2). In > like manner, a[0]['tuple'] = (1,2) is equivalent to b = a[0]; b['tuple'] = > (1,2). > > To understand the behavior, we need to dissect both code paths and what > happens. You built a (3,) array of those elements in 'a'. When you write > b = a['tuple'] you should probably be getting a (3,) array of (2,)-integers, > but as there is currently no formal dtype support for (n,)-integers as a > general dtype in NumPy, you get back a (3,2) array of integers which is the > closest thing that NumPy can give you. Setting the [0] row of this object > via > > a['tuple'][0] = (1,2) > > works just fine and does what you would expect. > > On the other hand, when you type: > > b = a[0] > > you are getting back an array-scalar which is a particularly interesting > kind of array scalar that can hold records. This new object is formally > of type numpy.void and it holds a "scalar representation" of anything that > fits under the "VOID" basic dtype. > > For some reason: > > b['tuple'] = [1,2] > > is not working. On my system I'm getting a different error: TypeError: > object of type 'int' has no len() > > I think this should be filed as a bug on the issue tracker which is for the > time being here: http://projects.scipy.org/numpy > > The problem is ultimately the void->copyswap function being called in > voidtype_setfields if someone wants to investigate. I think this behavior > should work. >
Just playing around I found this to be odd, though I guess makes some sense given your comments [~/] [12]: b['tuple'] = [(1,2)] [~/] [13]: b [13]: ([1, 0],) [~/] [14]: a [14]: array([([1, 0],), ([0, 0],), ([0, 0],)], dtype=[('tuple', '<i8', (2,))]) [~/] [15]: b[0].dtype [15]: dtype('int64') [~/] [16]: np.version.full_version [16]: '1.6.1' Skipper _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion