Mailman 3 September 2009 - NumPy-Discussion

Compact way of performing array math with specified result type?
by Russell E. Owen Feb. 8, 2010

Feb. 8, 2010

I often find myself doing simple math on sequences of numbers (which might or might not be numpy arrays) where I want the result (and thus the inputs) coerced to a particular data type. I'd like to be able to say: numpy.divide(seq1, seq2, dtype=float) but ufuncs don't allow on to specify a result type. So I do this instead: numpy.array(seq1, dtype=float) / numpy.array(seq2, dtype=float) Is there a more compact solution (without having to create the result array first and supply it as an argument)? -- Russell

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Assigning complex values to a real array
by Stéfan van der Walt Dec. 10, 2009

Dec. 10, 2009

Hi all, The following code succeeds, while I thought it should fail: a = np.zeros(6) # real b= np.arange(6)*(2+3j) # complex a[1] = b[1] # shouldn't this break? What is the rationale behind this behaviour? Cheers Stéfan

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Is anyone knowledgeable about dll deployment on windows ?
by David Cournapeau Dec. 1, 2009

Dec. 1, 2009

Hi, My head hurt trying to understand dll management with windows. I wanted to find a sane way to use dll for numscons, but I can't see how to do this, so I was wondering if anyone on this ML had any deep knowledge on how to install dll, and reuse them with python extensions ? The problem is the following: - you have some dll (say MKL) in a path (say C:\program files\MKL). - how do you tell another dll (more exactly a python extension, a .pyd) to look for mkl dll into the MKL path ? It seems that there is no rpath-like capability on windows, and the only way to load dll is to put them into some windows directory, or to put the dll path into PATH. Is it really the only way ? cheers, David

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Convert data into rectangular grid
by jah Oct. 5, 2009

Oct. 5, 2009

Hi, Suppose I have a set of x,y,c data (something useful for matplotlib.pyplot.plot() ). Generally, this data is not rectangular at all. Does there exist a numpy function (or set of functions) which will take this data and construct the smallest two-dimensional arrays X,Y,C ( suitable for matplotlib.pyplot.contour() ). Essentially, I want to pass in the data and a grid step size in the x- and y-directions. The function would average the c-values for all points which land in any particular square. Optionally, I'd like to be able to specify a value to use when there are no points in x,y which are in the square. Hope this makes sense.

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ufunc and errors
by Dag Sverre Seljebotn Oct. 3, 2009

Oct. 3, 2009

I looked and looked in the docs, but couldn't find an answer to this: When writing a ufunc, is it possible somehow to raise a Python exception (by acquiring the GIL first to raise it, set a flag and a callback which will be called with the GIL, or otherwise?). Or should one always use NaN even if the input does not make any sense (like, herhm, passing anything but integers or half-integers to a Wigner 3j symbol). I know how I'd to it manually in a wrapper w/ passed in context if not, but wanted to see. Also, will the arguments always be named x1, x2, x3, ..., or can I somehow give them custom names? Dag Sverre

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merging docs from wiki
by Ralf Gommers Oct. 2, 2009

Oct. 2, 2009

Hi, I'm done reviewing all the improved docstrings for NumPy, they can be merged now from the doc editor Patch page. Maybe I'll get around to doing the SciPy ones as well this week, but I can't promise that. There are a few docstrings on the Patch page I did not mark "Ok to apply": 1. the generic docstrings. Some are marked Ready for review, but they refer mostly to "self" and to "generic" which I don't think is very helpful. It would be great if someone could do just one of those docstrings and make it somewhat informative. There are about 50 that can then be done in the same way. 2. get_numpy_include: the docstring is deleted because the function is deprecated. I don't think that is helpful but I'm not sure. Should this be reverted or applied? Cheers, Ralf

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Question about improving genfromtxt errors
by Skipper Seabold Oct. 2, 2009

Oct. 2, 2009

There have been some recent attempts to improve the error reporting in genfromtxt <http://projects.scipy.org/numpy/ticket/1212>, which is great, because hunting down the problems reading in big and messy files is not fun. I am working on a patch that keeps up with the line number and column number of where you are in parsing the file, so that this can be reported in the error. Is there a way to catch a raised error and add to it? For instance, I have a problem in my file which leads to this error being raised from np.lib._iotools.StringCoverter.upgrade ValueError: Converter is locked and cannot be upgraded I added this into np.lib.io.genfromtxt around line 995. linenum = 0 [...] if dtype is None: try: colnum = 0 for (converter, item) in zip(converters, values): converter.upgrade(item) colnum += 1 except: raise ValueError, "I don't report the error from _iotools.StringConverter.upgrade, but I do know that there is a problem trying to convert a value at line %s and column %s" % (linenum,colnum) [...] linenum += 1 I'd like to add line and column number information to original error from _iotools. Any suggestions? Cheers, Skipper

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Deprecate chararray [was [SciPy-dev] Plea for help]
by David Goldsmith Oct. 1, 2009

Oct. 1, 2009

--- On Thu, 8/20/09, Christopher Hanley <chanley(a)stsci.edu> wrote: > I'd like to respectfully request that we move any > discussion of what > to do with the numpy.char module to the numpy list. NP, done. > I'm a little concerned about some of the assumptions that > are being > made about the number of users of the module. I would > also like to > better understand the reasons for wanting to dump it. I think Ralf did a pretty good job of synopsizing the reasons for deprecation, but since we're moving the thread, I'll reprint them here: 0) "it gets very little use" (an assumption you presumably dispute); 1) "is pretty much undocumented" (less true than a week ago, but still true for several of the attributes, with another handful or so falling into the category of "poorly documented"); 2) "probably more buggy than most other parts of NumPy" ("probably" being a euphemism, IMO); 3) "there is not a really good use-case for it" (a conjecture, but one that has yet to be challenged by counter-example); 4) it's not the first time its presence in NumPy has been questioned ("as Stefan pointed out when asking this same question last year") 5) NumPy already has a (perhaps superior) alternative ("object arrays would do nicely if one needs this functionality"); to which I'll add: 6) it is, on its face, "counter to the spirit" of NumPy. So far, IIRC, the only reason in favor of its continued inclusion is inertia. > Let me be > clear. I'm not opposed to change. However > breaking other people's > code just for the sake of change seems like a poor reason So, I don't think we're proposing this "just for the sake of change" > and a mean > thing to do to our customers. Apologies, but it is not proposed maliciously. The only other things I would add by way of "review" from the scipy-dev thread: a compromise proposal (made by Ralf): "Put clearly in the docs that this module exists for backwards compatibility reasons, and is not recommended for new development" and a clarification of deprecation process (provided by Robert): "[asked by the present author] How has deprecation in Numpy worked in the past - by dictum, vote, or consensus? [Robert's answer] Consensus or dictum without major objection. Voting is pointless except to inform one of those." Thanks for your time and consideration. David Goldsmith > Thank you for your time and help, > Chris > > > -- > Christopher Hanley > Senior Systems Software Engineer > Space Telescope Science Institute > 3700 San Martin Drive > Baltimore MD, 21218 > (410) 338-4338 > > On Aug 20, 2009, at 1:35 AM, Robert Kern wrote: > > > On Wed, Aug 19, 2009 at 20:03, David > > Goldsmith<d_l_goldsmith(a)yahoo.com> > wrote: > >> I'm going to take it a step further: "breakage" is > always the > >> deterrent to change, and yet "change we must" > (i.e., "adapt or > >> die"). It's certainly not without precedent > - even within Numpy, I > >> believe - for things (though perhaps not whole > namespaces) to be > >> deemed "to-be-deprecated," have a warning to this > effect > >> established in one x.[even #].0 release, and then > be removed by the > >> x.[even # + 2 or + 4].0 release. How has > deprecation in Numpy > >> worked in the past - by dictum, vote, or > consensus? > > > > Consensus or dictum without major objection. Voting is > pointless > > except to inform one of those. > > > > -- > > Robert Kern > > > > "I have come to believe that the whole world is an > enigma, a harmless > > enigma that is made terrible by our own mad attempt to > interpret it as > > though it had an underlying truth." > > -- Umberto Eco > > _______________________________________________ > > Scipy-dev mailing list > > Scipy-dev(a)scipy.org > > http://mail.scipy.org/mailman/listinfo/scipy-dev > > _______________________________________________ > Scipy-dev mailing list > Scipy-dev(a)scipy.org > http://mail.scipy.org/mailman/listinfo/scipy-dev >

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Another dumb structured array question
by David Warde-Farley Sept. 30, 2009

Sept. 30, 2009

Is there an easy way to get multiple subdtypes out? e.g. if I have a dtype dtype([('foo', 'i4'), ('bar', 'i8'), ('baz', 'S100')]) and an array with that dtype, is there a way to only get the 'foo' and 'bar'? arr[('foo','bar')] doesn't seem to work. David

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scipy.reddit.com
by David Warde-Farley Sept. 30, 2009

Sept. 30, 2009

In the spirit of the 'advice' site, and given that we're thinking of moving scipy.org to more static content (once I have some free time on my hands again, which should be soon!), I set up a 'subreddit' on reddit.com for Python-in-Science related links. I even came up with a somewhat spiffy logo for it. Think of it as a communal, collaboratively filtered (via up/down votes, using the arrows next to each submission) bookmarks folder/news site/etc. I'd encourage people to use it and add to it if they feel it might be of use to the community. The address is http://scipy.reddit.com/ , or equivalently http://www.reddit.com/r/scipy David

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