Re: [matplotlib-devel] propagation of error messages in matplotlib

[John H. <jdh...@ac...>]

>>>>> "Steve" == Steve Chaplin <ste...@ya...> writes:
    Steve> For an IOError the exception attribute 'filename' is set to
    Steve> the filename. With your example above
    Steve> self.renderer._renderer.write_png(str (filename)) is Agg
    Steve> C++ extension code The line fp = fopen(file_name, "wb");
    Steve> could be changed to something like if ((fp =
    Steve> fopen(file_name, "wb")) == NULL) throw Py::IOError("could
    Steve> not open file", filename);

    Steve> Does this look right John?

Right in principle, but not in practice.

For one thing, cxx strangely doesn't define an IOError.  I don't know
if this is simply an oversight.  Perhaps I'll file a bug on the sf
site....

The larger problem is that the exception constructor doesn't accept
multiple args and concatenate them.  It would be nice if it did.

I added a Printf class to mplutils to ease the burden of making printf
style strings in C++ to make better exceptions, and updated the
exceptions in the image, agg and ft2font extensions.  The standard
usage is

    if ((fp = fopen(file_name, "wb")) == NULL) 
      throw Py::RuntimeError( Printf("Could not open file %s", file_name).str() );

JDH