On 12/03/2012 07:16 PM, Nathaniel Smith wrote: > On Mon, Dec 3, 2012 at 11:50 PM, Chris Barker - NOAA Federal > <chris.bar...@noaa.gov> wrote: >> On Mon, Dec 3, 2012 at 2:21 PM, Nathaniel Smith <n...@pobox.com> wrote: >>> For the file handle, I would just write >>> >>> cdef FILE *fp = fdopen(file_obj.fileno(), "w") >>> >>> and be done with it. This will work with any version of Python etc. >> yeah, that makes sense -- though what if you want to be able to >> read_to/write_from a file that is already open, and in the middle of >> the file somewhere -- would that work? >> >> I just posted a question to the Cython list, and indeed, it looks like >> there is no easy answer to the file issue. > Yeah, this is a general problem with the Python file API, trying to > hook it up to stdio is not at all an easy thing. A better version of > this code would skip that altogether like: > > cdef void write_to_pyfile(png_structp s, png_bytep data, png_size_t count): > fobj = <object>png_get_io_ptr(s) > pydata = PyString_FromStringAndSize(data, count) > fobj.write(pydata) > > cdef void flush_pyfile(png_structp s): > # Not sure if this is even needed > fobj = <object>png_get_io_ptr(s) > fobj.flush() > > # in write_png: > write_png_c(<png_byte*>pix_buffer, width, height, > NULL, <void*>file_obj, write_to_pyfile, flush_pyfile, dpi)
This is what my original version already does in the event that the file_obj is not a "real" file. In practice, you need to support both methods -- the callback approach is many times slower than writing directly to a regular old FILE object, because there is overhead both at the libpng and Python level, and there's no way to select a good buffer size. > > But this is a separate issue :-) (and needs further fiddling to make > exception handling work). > > Or if you're only going to work on real OS-level file objects anyway, > you might as well just accept a filename as a string and fopen() it > locally. Having Python do the fopen just makes your life harder for no > reason. There's actually a very good reason. It is difficult to deal with Unicode in file paths from C in a portable way. On Windows, for example, if the user's name contains non-ascii characters, you can't write to the home directory using fopen, etc. It's doable with some care by using platform-specific C APIs etc., but CPython has already done all of the hard work for us, so it's easiest just to leverage that by opening the file from Python. Mike ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Matplotlib-devel mailing list Matplotlib-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
