matplotlib-devel

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

[Jochen V. <vo...@se...>]

Hello,

On Fri, Nov 19, 2004 at 10:33:43AM -0600, John Hunter wrote:
> >>>>> "Jochen" =3D=3D Jochen Voss <vo...@se...> writes:
>     Jochen> Slight problem: it might now be a little bit more
>     Jochen> difficult to include the name of the file which could not
>     Jochen> be opened in the error message.  The IOError exception
>     Jochen> will probably only have "permission denied" associated
>     Jochen> with it.
>=20
> Looks OK, at least on linux
>=20
>=20
> >>> file('/sbin/ldconfig', 'w')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> IOError: [Errno 13] Permission denied: '/sbin/ldconfig'

But sometimes it doesn't give the file name:

    >>> from matplotlib.matlab import *
    >>> plot([1,2,3],[2,3,1])
    [<matplotlib.lines.Line2D instance at 0x41ef774c>]
    >>> savefig("/forbidden.png")
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
      File ".../matlab.py", line 1009, in savefig
        manager.canvas.print_figure(*args, **kwargs)
      File ".../backends/backend_gtkagg.py", line 69, in print_figure
        agg.print_figure(filename, dpi, facecolor, edgecolor, orientation)
      File ".../backends/backend_agg.py", line 379, in print_figure
        self.renderer._renderer.write_png(str(filename))
    RuntimeError: could not open file

I did not investigate what happens here, but if there is an easy way to
get the file name into the exception we should probably use it.

All the best,
Jochen
--=20
http://seehuhn.de/

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

[Steve C. <ste...@ya...>]

On Wed, 2004-11-24 at 12:06 +0000, Jochen Voss wrote:
> Hello,
> 
> On Fri, Nov 19, 2004 at 10:33:43AM -0600, John Hunter wrote:
> > >>>>> "Jochen" == Jochen Voss <vo...@se...> writes:
> >     Jochen> Slight problem: it might now be a little bit more
> >     Jochen> difficult to include the name of the file which could not
> >     Jochen> be opened in the error message.  The IOError exception
> >     Jochen> will probably only have "permission denied" associated
> >     Jochen> with it.
> > 
> > Looks OK, at least on linux
> > 
> > 
> > >>> file('/sbin/ldconfig', 'w')
> > Traceback (most recent call last):
> >   File "<stdin>", line 1, in ?
> > IOError: [Errno 13] Permission denied: '/sbin/ldconfig'
> 
> But sometimes it doesn't give the file name:
> 
>     >>> from matplotlib.matlab import *
>     >>> plot([1,2,3],[2,3,1])
>     [<matplotlib.lines.Line2D instance at 0x41ef774c>]
>     >>> savefig("/forbidden.png")
>     Traceback (most recent call last):
>       File "<stdin>", line 1, in ?
>       File ".../matlab.py", line 1009, in savefig
>         manager.canvas.print_figure(*args, **kwargs)
>       File ".../backends/backend_gtkagg.py", line 69, in print_figure
>         agg.print_figure(filename, dpi, facecolor, edgecolor, orientation)
>       File ".../backends/backend_agg.py", line 379, in print_figure
>         self.renderer._renderer.write_png(str(filename))
>     RuntimeError: could not open file
> 
> I did not investigate what happens here, but if there is an easy way to
> get the file name into the exception we should probably use it.
> 
> All the best,
> Jochen
For an IOError the exception attribute 'filename' is set to the
filename. With your example above self.renderer._renderer.write_png(str
(filename)) is Agg C++ extension code
The line
 fp = fopen(file_name, "wb");
could be changed to something like
 if ((fp = fopen(file_name, "wb")) == NULL)
     throw Py::IOError("could not open file", filename);

Does this look right John?

Steve

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

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

[Steve C. <ste...@ya...>]

On Wed, 2004-11-24 at 09:34 -0600, John Hunter wrote:
> 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 Python C API uses 
PyErr_SetFromErrnoWithFilename(PyObject *type, char *filename)
to raise IOError exceptions, perhaps cxx has an equivalent function.

Steve