Raising a specific OSError

[David Hirschfield]

I know this should be obvious, but how does one raise a specific type of
OSError?
When I attempt to perform a file operation on a non-existent file, I get
an OSError: [Errno 2], but what if I want to raise one of those myself?

Thanks in advance,
-Dave

 

[alisonken1]

To raise a specific error, just find the error that you want to raise,
then give the error a text string to print: ex.

raise IOError("This raises an IO error")

Traceback (most recent call last):

Just be sure of the error that you want to raise, since some of them
will do stuff like closing open file descriptors as well.

 

[Kelvie Wong]

I do not see the point in doing so (why not just copy+paste that
string?), but the errno (specifically ENOENT) corresponds to the
POSIX.1 error number, and the string "No such file or directory" is
done in C via strerror(ENOENT); (check errno(3) and strerror(3)).

I doubt there is something that does this in the standard library
(just checked, there's an errno module, but it is quite sparse), but a
simple C extension would be trivial to write.

However, the best way is just to copy and paste that text into your
program, I mean, why not?

raise OSError("[Errno 2] No such file or directory")

I wasn't clear enough in my original post.

I know how to raise a basic OSError or IOError, but what if I want to raise
specifically an "OSError: [Errno 2] No such file or directory"?
Somehow it must be possible to raise the error with the correct information
to bring up the standard message, but where do I find the right values to
give?

Thanks,
-Dave



alisonken1 wrote:
To raise a specific error, just find the error that you want to raise,
then give the error a text string to print: ex.

raise IOError("This raises an IO error")

On the stderr output, when the routine hits this line, you will get:





raise IOError("This raises an IOError")

Traceback (most recent call last):
File "<stdin>", line 1, in ?
IOError: This raises an IOError


Just be sure of the error that you want to raise, since some of them
will do stuff like closing open file descriptors as well.

 

[Kelvie Wong]

Looking at the Python docs.. I found this:
http://docs.python.org/ext/errors.html

"""
Another useful function is PyErr_SetFromErrno(), which only takes an
exception argument and constructs the associated value by inspection
of the global variable errno. The most general function is
PyErr_SetObject(), which takes two object arguments, the exception and
its associated value. You don't need to Py_INCREF() the objects passed
to any of these functions.
"""

So, in a C extension, to raise a a specific OSError...

errno = ENOENT;
PyErr_SetFromErrno(PyExc_OSError);

should work...

I do not see the point in doing so (why not just copy+paste that
string?), but the errno (specifically ENOENT) corresponds to the
POSIX.1 error number, and the string "No such file or directory" is
done in C via strerror(ENOENT); (check errno(3) and strerror(3)).

I doubt there is something that does this in the standard library
(just checked, there's an errno module, but it is quite sparse), but a
simple C extension would be trivial to write.

However, the best way is just to copy and paste that text into your
program, I mean, why not?

raise OSError("[Errno 2] No such file or directory")

I wasn't clear enough in my original post.

I know how to raise a basic OSError or IOError, but what if I want to raise
specifically an "OSError: [Errno 2] No such file or directory"?
Somehow it must be possible to raise the error with the correct information
to bring up the standard message, but where do I find the right values to
give?

Thanks,
-Dave



alisonken1 wrote:
To raise a specific error, just find the error that you want to raise,
then give the error a text string to print: ex.

raise IOError("This raises an IO error")

On the stderr output, when the routine hits this line, you will get:





raise IOError("This raises an IOError")

Traceback (most recent call last):
File "<stdin>", line 1, in ?
IOError: This raises an IOError


Just be sure of the error that you want to raise, since some of them
will do stuff like closing open file descriptors as well.

 

[Lawrence D'Oliveiro]

When I attempt to perform a file operation on a non-existent file, I get
an OSError: [Errno 2], but what if I want to raise one of those myself?

raise OSError(2, "No such file or directory")