Module _gmp.gmp_error

We gently trap errors generated by the GNU MP library. When the latter sends the SIGFPE (Floating Point Error) signal following a fatal error (division by zero, for example), the gmp module captures this signal and raises an appropriate exception without aborting the Python interpreter. Let’s look at some examples:

>>> z = mpz(-1); u = mpz()
>>> z.sqrt()
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    z.sqrt()
    ~~~~~~^^
_gmp.gmp_error: square root of negative (gmp_errno=4)
>>> z // u
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    z // u
    ~~^^~~
_gmp.gmp_error: division by zero (gmp_errno=2)
>>> # Python interpreter still alive - no abort()

Same example using a block try / except:

>>> z = mpz(-1); u = mpz()
>>> try:
...     z.sqrt()
... except GMPErrSqrtOfNegative:
...     # Do something.
>>> try:
...     z // u
... except GMPErrDivisionByZero:
...     # Do something.
>>> # Python interpreter still alive - no abort()

Warning

The trick is, after capturing the SIGFPE signal, to perform a non-local goto using system calls sigsetjmp() and siglongjmp(), which of course assumes that these are present on the operating system (which should be the case for any system conforming to the standard POSIX.1-2008).

Exceptions generated by the GNU MP library

exception _gmp.gmp_error.GMPErrUnsupportedArgument

exception _gmp.gmp_error.GMPErrDivisionByZero

exception _gmp.gmp_error.GMPErrSqrtOfNegative

exception _gmp.gmp_error.GMPErrInvalidArgument

exception _gmp.gmp_error.GMPErrMPZOverflow

Mapping table between _gmp.gmp_error errors and GMP MP errors

_gmp.gmp_error Error	GNU MP Error (defined in <gmp.h>)
GMPErrUnsupportedArgument	GMP_ERROR_UNSUPPORTED_ARGUMENT
GMPErrDivisionByZero	GMP_ERROR_DIVISION_BY_ZERO
GMPErrSqrtOfNegative	GMP_ERROR_SQRT_OF_NEGATIVE
GMPErrInvalidArgument	GMP_ERROR_INVALID_ARGUMENT
GMPErrMPZOverflow	GMP_ERROR_MPZ_OVERFLOW.