Let us say that we want a slightly more relaxed policy than the standard RExec class. For example, if we're willing to allow files in "/tmp" to be written, we can subclass the RExec class:
class TmpWriterRExec(rexec.RExec):
def r_open(self, file, mode='r', buf=-1):
if mode in ('r', 'rb'):
pass
elif mode in ('w', 'wb', 'a', 'ab'):
# check filename : must begin with /tmp/
if file[:5]!='/tmp/':
raise IOError, "can't write outside /tmp"
elif (string.find(file, '/../') >= 0 or
file[:3] == '../' or file[-3:] == '/..'):
raise IOError, "'..' in filename forbidden"
else: raise IOError, "Illegal open() mode"
return open(file, mode, buf)