We are announcing the availability of PyFITS, a Python module to provide a means of reading and writing FITS format files. The FITS (Flexible Image Transport System) format is standardized data format widely used for astronomical data (http://fits.gsfc.nasa.gov/). This module is based on the PyFITS module initially developed by Paul Barrett while he was at NASA/Goddard but has since been modified and adapted for use by the Space Telescope Science Institute. It has been developed primarily by Paul Barrett, Jin-Chung Hsu, and Todd Miller, with assistance from Warren Hack, Phil Hodge, and Michele De La Pena. It is being released under an Open Source License. A web page for PyFITS is available: http://stsdas.stsci.edu/pyfits There is a preliminary draft for a PyFITS manual available from that page. It is still in the early stages and is incomplete (particularly with regard to the details of how to manipulate table objects). However, there should be enough information to indicate how to perform basic operations with FITS files. PyFITS requires that numarray v0.2 be installed (http://stsdas.stsci.edu/numarray). Numarray is a relatively new replacement for the Numeric module (and largely backward- compatible at the Python level). It also currently lacks all of the 3rd-party libraries that Numeric has (this will begin to change within a couple of months). However, it is not compatible at the C-API level nor are numarray and Numeric arrays interchangeable. It is possible to have both modules loaded simultaneously and to convert between numarray and Numeric arrays using the tostring/fromstring mechanism each provides (at the expense of extra memory usage, of course) The PyFITS module is simply a single Python file (pyfits.py). Installation consists of placing that file in a directory in the Python search path. Besides the use of numarray, there are significant differences with the interface provided by the original PyFITS. We do not expect many future backward-incompatible changes to the interface of PyFITS. (Though more methods and functions will almost certainly be added.) This is an early version and undoubtably bugs will be discovered when used with a greater variety of FITS files. Currently PyFITS take a fairly strict interpretation of FITS files. There are likely to be problems with FITS data that do not strictly conform to the standard. We intend to accommodate such variances, particularly if they involve widely used or available data (so please let us know when such problems occur). Things not yet supported but are part of future development: 1) Verification and/or correction of FITS objects being written to disk so that they are legal FITS. This is being added now and should be available in about a month. Currently, one may construct FITS headers that are inconsistent with the data and write such FITS objects to disk. Future versions will provide options to either a) correct discrepancies and warn, b) correct discrepancies silently, c) throw a Python exception, or d) write illegal FITS (for test purposes!). 2) Support for ascii tables or random groups format. Support for ASCII tables will be done soon (~1 month). When random group support is added is uncertain. 3) Support for memory mapping FITS data (to reduce memory demands). We expect to provide this capability in about 3 months. 4) Support for columns in binary tables having scaled values (e.g. BSCALE or BZERO) or boolean values. Currently booleans are stored as Int8 arrays and users must explicitly convert them into a boolean array. Likewise, scaled columns must be copied with scaling and offset by testing for those attributes explicitly. Future versions will produce such copies automatically. 5) Support for tables with TNULL values. This awaits an enhancement to numarray to support mask arrays (planned). (At least a couple months off) Please contact help@stsci.edu for with questions about it usage, bug reports, or requests for enhancements. Perry Greenfield Science Software Group