Catching Python's OverflowError after some dumb calculation, I checked the error's args and saw it's a tuple containing an integer as its first coordinate. I assume this is some kind of error number (errno). However, I could not find any documentation or reference for it.
Example:
try:
1e4**100
except OverflowError as ofe:
print ofe.args
## prints '(34, 'Numerical result out of range')'
Do you know what 34 means in this context? Do you know other possible error numbers for this exception?
There is a module in the standard library called errno:
This module makes available standard errno system symbols. The value of each symbol is the corresponding integer value. The names and descriptions are borrowed from linux/include/errno.h, which should be pretty all-inclusive.
/usr/include/linux/errno.h includes /usr/include/asm/errno.h that includes /usr/include/asm-generic/errno-base.h.
me@my_pc:~$ cat /usr/include/asm-generic/errno-base.h | grep 34
#define ERANGE 34 /* Math result not representable */
Now we know that the 34 error code stands for ERANGE.
1e4**100 is processed with float_pow function from Object/floatobject.c. Partial source code of that function:
static PyObject *
float_pow(PyObject *v, PyObject *w, PyObject *z)
{
// 107 lines omitted
if (errno != 0) {
/* We do not expect any errno value other than ERANGE, but
* the range of libm bugs appears unbounded.
*/
PyErr_SetFromErrno(errno == ERANGE ? PyExc_OverflowError :
PyExc_ValueError);
return NULL;
}
return PyFloat_FromDouble(ix);
}
So, 1e4**100 causes ERANGE error (resulting in PyExc_OverflowError) and then the higher level OverflowError exception raises.