import ipaddress


def get_prefix_with_offset(base, offset):
    """Compute prefix from base prefix plus offset.

    >>> get_prefix_with_offset(ipaddress.ip_network("10.0.0.0/16"), 0)
    IPv4Network('10.0.0.0/16')
    >>> get_prefix_with_offset(ipaddress.ip_network("10.0.0.0/16"), 3)
    IPv4Network('10.3.0.0/16')
    """
    return ipaddress.ip_network("{}/{}".format(
        base[0] +
        base.num_addresses * offset,
        base.prefixlen))