Mailman 3 February 2012 - AstroPy

Astropy website/logo competition!
by Thomas Robitaille March 19, 2012

March 19, 2012

Hi everyone, We are holding a design competition for the http://www.astropy.org website and logo! There is a prize of a $50 (or equivalent) Amazon Voucher for the winner, and the deadline for submissions is March 31st 2012. Instructions and guidelines can be found at the following page: http://github.com/astropy/astropy/wiki/Website-logo-competition Please let us know if you have any questions. We look forward to your submissions! Cheers, Tom

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strange error with ctypes
by Jerome Caron Feb. 20, 2012

Feb. 20, 2012

Dear list, I am developping since 2 years a library for photometry in Python. Everything is here: www.aspylib.com At the moment I have a very strange bug and no idea how to solve it, so I am asking for some help... or recommendations about a better place to ask for help (a different list ?) My OS is Windows XP. The Python script is calling a few dll (written in C++) that are interfaced with ctypes. Looking at the messages in the Python console the error occurs when calling one of these dll (this particular dll is called several hundreds of thousands of times without error just before, and this time there is an error..). The error message is something like: File "C:\Documents and Settings\jerome caron\My Documents\Python2\aspylib\astro\transform.py", line 35, in translate_Bspline cdll.Bspline.Translate(dim,dim_x,dim_y,indata,dxy,spline_degree,outdata) WindowsError: exception: access violation reading 0x4158B870 The Python code that calls the dll is (I changed it many time without resolving the error) if len(images.shape)==2: dim = 1 dim_x, dim_y = images.shape else: dim, dim_x, dim_y = images.shape indata = np.ascontiguousarray(np.array(images, dtype = np.float32)) dxy = np.ascontiguousarray(np.array(shift, dtype = np.float32)) outdata = np.ascontiguousarray(np.empty(images.shape, dtype = np.float32)) cdll.Bspline.Translate.argtypes = [c_long, c_long, c_long, ndpointer(dtype=np.float32), ndpointer(dtype=np.float32), c_long, ndpointer(dtype=np.float32)] cdll.Bspline.Translate(dim,dim_x,dim_y,indata,dxy,spline_degree,outdata) The dll prototype in C is int Translate(int dim, int dim_x, int dim_y, float* a, float* shifts, int spline_degree, float* b); So everything looks ok and I would suspect an error in the C++ code. But here comes the nasty thing. The code in the dll is very basic and clean. Actually it does not throw any exception as I checked by inserting a try..catch statement try{ all the dll code here} catch(...){printf("there was an error ni the dll!");} Investigating further, the error occurs when executing a free() instruction. I don't see how this could create an error ! The piece of C code looks like Line = (double *)malloc((size_t)(Width * (long)sizeof(double))); if (Line == (double *)NULL) { printf("Row allocation failed\n"); return(1); } for (y = 0L; y < Height; y++) { GetRow(Image, y, Line, Width); ConvertToInterpolationCoefficients(Line, Width, Pole, NbPoles, DBL_EPSILON); PutRow(Image, y, Line, Width); } free(Line); And the error occurs at the statement free(Line). I am starting to suspect something nasty happening with ctypes. Or maybe I am missing something very basic ? Any suggestion ? I am sure there are experienced programmers on this list, who could advice me. Many thanks for your help and patience reading me Kind regards Jerome Caron

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Refractive index calculations (feedback request)
by Prasanth Feb. 16, 2012

Feb. 16, 2012

Hello, I have written a module in Python for calculating refractive index under different environmental conditions, and for converting wavelength of light between air and vacuum. The code is based on the documentation for the NIST online refractive index of air calculator<http://emtoolbox.nist.gov/Wavelength/Documentation.asp> . It would be great to know how this compares to existing tools used by astronomers in their research level code. The function "ref_index._test_idlastro()" includes some comparison with IDLASTRO vac2air and air2vac procedures. The module is available at http://pypi.python.org/pypi/ref_index. It has no dependencies outside of standard Python libraries. It can be installed using "pip install ref_index". Documentation is available within the source code, and it can also be displayed in interactive Python/iPython session by typing "help(ref_index)" after importing ref_index. All functions also have documentation. The development repository is at https://github.com/phn/ref_index . Thanks Prasanth

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Using MacPorts for Python
by Thomas Robitaille Feb. 2, 2012

Feb. 2, 2012

Hi Everyone, Earlier this year I was given commit privileges to the MacPorts (http://www.macports.org/) package index, and I've already added a few Astronomy Python packages. After moved between various install methods in the last couple of years (system Python, EPD, source install, python.org distribution, ...) I've now settled on using the Python distribution from MacPorts. One of my main reasons for doing this is that I needed some complex packages (Qt and GTK+) which are not included in EPD, and by far the easiest way to install them has been through MacPorts. However, I believe a MacPorts Python distribution can still be very useful even if you don't need these packages, so I've compiled a list of simple instructions to set up a full Python distribution using MacPorts on Mac: http://astrofrog.github.com/macports-python/ Updating packages is easy, and dependencies are automatically taken care of. For now I recommend using Python 2.7 as indicated in the instructions. I would welcome any feedback, especially if you run into issues, and would also welcome suggestions for other packages to add. For new packages you can either email me directly or open a ticket on MacPorts and cc robitaille(a)macports.org on the ticket. To report issues with the instructions, open an issue at: https://github.com/astrofrog/macports-python Note that it's possible/easy to install several Python versions with MacPorts at the same time and you can switch which one is the default with 'port select', or call the version you want directly with ipython-3.1 for example. This makes it ideal if you want to be able to test your code using different python versions or want to experiment with Python 3. Cheers, Thomas

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