'return the DNS PTR string of the provided IP address object
If "suffix" is provided it will be appended as the second and top
level reverse domain.
If omitted it is implicitly set to the second and top level reverse
domain of the according IP address family'

def getPTR(self, suffix=None):

    if self.isIPv4:
        exploded_ip = self.ntoa.split('.')
        if (suffix is None):
            suffix = 'in-addr.arpa.'
    elif self.isIPv6:
        exploded_ip = self.hexdump
        if (suffix is None):
            suffix = 'ip6.arpa.'
    else:
        return ''
    return ('%s.%s' % ('.'.join(reversed(exploded_ip)), suffix))
