def exists(args, key):
    if key in args:
        return args[key]
    else:
        raise ArgumentError(_('Argument %s is required.') % key)
Write your forwards methods here.
dataset/ETHPy150Open nii-cloud/dodai-compute/plugins/xenserver/xenapi/etc/xapi.d/plugins/pluginlib_nova.py/exists--crossover with--dataset/ETHPy150Open stephenmcd/gnotty/gnotty/migrations/0003_joins_leaves.py/Migration.forwards