The SIGXFSZ signal is sent when the maximum file size limit is
exceeded (RLIMIT_FSIZE).  Apparently, it is also sent when the 2GB
file limit is reached on platforms without large file support.

The default action for SIGXFSZ is to terminate the process and dump
core.  When it is ignored, the system call that caused the limit to be
exceeded returns an error and sets errno to EFBIG.  Python
always checks errno on I/O syscalls, so there is nothing to do with
the signal.